The binding of cholera toxin to three transformed mouse cell lines derived from the same parent strain, and the effects of the toxin on DNA synthesis and adenylate cyclase activity, vary in parallel with the ganglioside composition of the cells. TAL/N cells of early passage, which contain large quantities of gangliosides G(M3), G(M2), G(M1), and G(Dla), as well as the glycosyltransferases necessary for the synthesis of these gangliosides, bind the most cholera toxin and are the most sensitive to its action. TAL/N cells of later passage, which lack chemically detectable G(M1) and G(Dla) and which have no UDP-Gal:G(M2) galactosyltransferase activity, are intermediate in binding and response to the toxin. SVS AL/N cells, which lack G(M2) in addition to G(M1) and G(Dla) and which have little detectable UDP-GalNAc:G(M3)N-acetylgalactosaminyltransferase activity, bind the least amount of toxin. The SVS AL/N cells are the least responsive to inhibition of DNA synthesis and stimulation of adenylate cyclase activity by cholera toxin. Gangliosides (especially G(M1)), which appear to be the natural membrane receptors for cholera toxin, may normally have important roles in the regulation of cell growth and cAMP-mediated responses.