The authors isolated six monoclonal antibodies (MAbs) from mice immunized with synthetic peptides derived from the human c-myc gene product. Five of these MAbs precipitate p62c-myc from human cells, and three of these also recognize the mouse c-myc gene product. None of the antibodies recognize the chicken p110c-myc protein. All six MAbs recognize immunoblotted p62c-myc, and they can be used to quantitate p62c-myc levels in cells. The MAbs are of the IgG1.k subclass and have high affinity for p62c-myc, as evidenced by their long dissociation half-lives. The MAbs recognize two different and discontinuous sequences on the intact human c-myc protein, suggesting that they bind to distinct epitopes. The MAbs are useful for immunoprecipitation and immunoblotting analyses of p62c-myc in cells, and preliminary data suggest their potential use in immunohistochemical analysis of p62c-myc in normal and neoplastic tissues. The availability of these reagents will facilitate further investigations into the function and pathology of c-myc expression in normal and neoplastic cells.The authors isolated six monoclonal antibodies (MAbs) from mice immunized with synthetic peptides derived from the human c-myc gene product. Five of these MAbs precipitate p62c-myc from human cells, and three of these also recognize the mouse c-myc gene product. None of the antibodies recognize the chicken p110c-myc protein. All six MAbs recognize immunoblotted p62c-myc, and they can be used to quantitate p62c-myc levels in cells. The MAbs are of the IgG1.k subclass and have high affinity for p62c-myc, as evidenced by their long dissociation half-lives. The MAbs recognize two different and discontinuous sequences on the intact human c-myc protein, suggesting that they bind to distinct epitopes. The MAbs are useful for immunoprecipitation and immunoblotting analyses of p62c-myc in cells, and preliminary data suggest their potential use in immunohistochemical analysis of p62c-myc in normal and neoplastic tissues. The availability of these reagents will facilitate further investigations into the function and pathology of c-myc expression in normal and neoplastic cells.