The article by Ewald R. Weibel, Gonzague S. Kistler, and Walter F. Scherle presents practical stereological methods for morphometric cytology, focusing on the determination of quantitative parameters of tissue structure using electron microscopy. The authors review and present general principles for estimating volumetric ratios, surface areas, surface-to-volume ratios, thicknesses of tissue or cell sheets, and the number of structures. They discuss the systematic and statistical errors involved in such measurements and outline practical application methods. The article emphasizes the importance of random sampling and the use of test systems, such as point lattices and test lines, to derive information from sections. Specific examples are provided for light and electron microscopy, including the determination of surface areas, surface-to-volume ratios, and the number of particulate structures. The authors also discuss the calibration and data recording processes, and conclude that stereological methods provide efficient and reliable tools for producing quantitative data on tissue structure, which can be subjected to statistical analysis to test for errors.The article by Ewald R. Weibel, Gonzague S. Kistler, and Walter F. Scherle presents practical stereological methods for morphometric cytology, focusing on the determination of quantitative parameters of tissue structure using electron microscopy. The authors review and present general principles for estimating volumetric ratios, surface areas, surface-to-volume ratios, thicknesses of tissue or cell sheets, and the number of structures. They discuss the systematic and statistical errors involved in such measurements and outline practical application methods. The article emphasizes the importance of random sampling and the use of test systems, such as point lattices and test lines, to derive information from sections. Specific examples are provided for light and electron microscopy, including the determination of surface areas, surface-to-volume ratios, and the number of particulate structures. The authors also discuss the calibration and data recording processes, and conclude that stereological methods provide efficient and reliable tools for producing quantitative data on tissue structure, which can be subjected to statistical analysis to test for errors.