Six monoclonal antibodies (MAbs) specific for human c-myc gene products were isolated from mice immunized with synthetic peptide immunogens derived from the human c-myc gene product. Five of these MAbs precipitate p62c-myc from human cells, and three also recognize the mouse c-myc gene product. None of the antibodies recognize the chicken p110gag-myc protein. All six MAbs recognize immunoblotted p62c-myc. These reagents allow quantification of p62c-myc in cells. The human c-myc proto-oncogene is the human homolog of the avian v-myc gene in retroviruses. Aberrant c-myc expression is implicated in various neoplasms. The human c-myc gene has been sequenced, and a 439-amino-acid product is inferred. Synthetic peptides were constructed from the gene sequence and used as immunogens. Antibodies raised against these peptides identify the human c-myc product as a 62-kDa protein. To develop better reagents for studying c-myc, six MAbs specific for two synthetic peptides from p62c-myc were isolated. These MAbs recognize p62c-myc in immunoblots and immunoprecipitation. The MAbs are of the IgG1 subclass and have high affinity for p62c-myc. Three MAbs recognize the chicken p110gag-myc protein, while others do not. The MAbs recognize different regions of p62c-myc, and all bind the same 62-kDa protein, suggesting it is the human c-myc product. The MAbs were used to analyze p62c-myc levels in various cell lines. Cells with amplified c-myc genes have higher p62c-myc levels. The levels of p62c-myc and c-myc mRNA vary among cell lines. In HL60 cells, DMSO-induced differentiation reduces c-myc mRNA and p62c-myc levels. The MAbs are useful for immunoprecipitation and immunoblotting. They may also be used in immunohistological analysis of p62c-myc in tissues. These reagents facilitate studies on c-myc function and pathology in normal and neoplastic cells.Six monoclonal antibodies (MAbs) specific for human c-myc gene products were isolated from mice immunized with synthetic peptide immunogens derived from the human c-myc gene product. Five of these MAbs precipitate p62c-myc from human cells, and three also recognize the mouse c-myc gene product. None of the antibodies recognize the chicken p110gag-myc protein. All six MAbs recognize immunoblotted p62c-myc. These reagents allow quantification of p62c-myc in cells. The human c-myc proto-oncogene is the human homolog of the avian v-myc gene in retroviruses. Aberrant c-myc expression is implicated in various neoplasms. The human c-myc gene has been sequenced, and a 439-amino-acid product is inferred. Synthetic peptides were constructed from the gene sequence and used as immunogens. Antibodies raised against these peptides identify the human c-myc product as a 62-kDa protein. To develop better reagents for studying c-myc, six MAbs specific for two synthetic peptides from p62c-myc were isolated. These MAbs recognize p62c-myc in immunoblots and immunoprecipitation. The MAbs are of the IgG1 subclass and have high affinity for p62c-myc. Three MAbs recognize the chicken p110gag-myc protein, while others do not. The MAbs recognize different regions of p62c-myc, and all bind the same 62-kDa protein, suggesting it is the human c-myc product. The MAbs were used to analyze p62c-myc levels in various cell lines. Cells with amplified c-myc genes have higher p62c-myc levels. The levels of p62c-myc and c-myc mRNA vary among cell lines. In HL60 cells, DMSO-induced differentiation reduces c-myc mRNA and p62c-myc levels. The MAbs are useful for immunoprecipitation and immunoblotting. They may also be used in immunohistological analysis of p62c-myc in tissues. These reagents facilitate studies on c-myc function and pathology in normal and neoplastic cells.