The plasma membrane contains lateral assemblies of glycolipids and cholesterol, called "rafts," which are involved in cellular processes such as membrane sorting, signal transduction, and cell adhesion. This study investigated the structure of raft domains in the plasma membrane of non-polarized cells. Overexpressed plasma membrane markers were evenly distributed in the plasma membrane. The patching behavior of pairs of raft markers was compared with pairs of raft/non-raft markers. The patches of these raft markers overlapped extensively in BHK cells and Jurkat T-lymphoma cells. The functional significance of lipid diversity in cell biological processes is now being unraveled. Recent developments show the involvement of specific lipids and lipid derivatives in membrane structure and dynamics. For example, phosphoinositides have been shown to be important mediators of membrane-cytoskeleton interactions and vesicular transport. Additionally, there is evidence for a role of phosphatidic acid in the formation of specific coats mediating the formation of transport vesicles. Considerable attention has recently been drawn to lateral assemblies of glycosphingolipids and cholesterol (termed rafts), which have been proposed to form platforms for numerous cellular events including membrane trafficking, signaling, and cell adhesion. The study shows that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. This view is supported by the finding that cholesterol depletion abrogated segregation. Our results are consistent with the view that raft domains in the plasma membrane of non-polarized cells are normally small and highly dispersed but that raft size can be modulated by oligomerization of raft components. The study also shows that patches of GPI-anchored PLAP accumulated src-like protein tyrosine kinase fyn, which is thought to be anchored in the cytoplasmic leaflet of raft domains. In contrast, patches of transferrin receptor as a non-raft marker were sharply separated. Taken together, our data strongly suggest that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. The study also shows that the copatching of HA and PLAP is independent of caveolae. The copatching of HA and PLAP is mostly found at non-invaginated regions of the plasma membrane. Thus the copatching of HA and PLAP cannot be explained by parallel movement of the two raft markers into caveolae as described previously for co-clustering of two different GPI-anchored proteins. The study also shows that antibody-induced cross-linking stabilizes membrane domains. Triton X-100 insolubility has been used as a diagnostic tool to identify raft membrane proteins. The study shows that detergent insolubility is related to antibody-induced patching, which is usedThe plasma membrane contains lateral assemblies of glycolipids and cholesterol, called "rafts," which are involved in cellular processes such as membrane sorting, signal transduction, and cell adhesion. This study investigated the structure of raft domains in the plasma membrane of non-polarized cells. Overexpressed plasma membrane markers were evenly distributed in the plasma membrane. The patching behavior of pairs of raft markers was compared with pairs of raft/non-raft markers. The patches of these raft markers overlapped extensively in BHK cells and Jurkat T-lymphoma cells. The functional significance of lipid diversity in cell biological processes is now being unraveled. Recent developments show the involvement of specific lipids and lipid derivatives in membrane structure and dynamics. For example, phosphoinositides have been shown to be important mediators of membrane-cytoskeleton interactions and vesicular transport. Additionally, there is evidence for a role of phosphatidic acid in the formation of specific coats mediating the formation of transport vesicles. Considerable attention has recently been drawn to lateral assemblies of glycosphingolipids and cholesterol (termed rafts), which have been proposed to form platforms for numerous cellular events including membrane trafficking, signaling, and cell adhesion. The study shows that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. This view is supported by the finding that cholesterol depletion abrogated segregation. Our results are consistent with the view that raft domains in the plasma membrane of non-polarized cells are normally small and highly dispersed but that raft size can be modulated by oligomerization of raft components. The study also shows that patches of GPI-anchored PLAP accumulated src-like protein tyrosine kinase fyn, which is thought to be anchored in the cytoplasmic leaflet of raft domains. In contrast, patches of transferrin receptor as a non-raft marker were sharply separated. Taken together, our data strongly suggest that coalescence of cross-linked raft elements is mediated by their common lipid environments, whereas separation of raft and non-raft patches is caused by the immiscibility of different lipid phases. The study also shows that the copatching of HA and PLAP is independent of caveolae. The copatching of HA and PLAP is mostly found at non-invaginated regions of the plasma membrane. Thus the copatching of HA and PLAP cannot be explained by parallel movement of the two raft markers into caveolae as described previously for co-clustering of two different GPI-anchored proteins. The study also shows that antibody-induced cross-linking stabilizes membrane domains. Triton X-100 insolubility has been used as a diagnostic tool to identify raft membrane proteins. The study shows that detergent insolubility is related to antibody-induced patching, which is used