Sodium butyrate and dimethylsulfoxide (DMSO) have marked effects on the growth, morphology, and biochemistry of two human colonic adenocarcinoma cell lines in culture. Doubling times were increased between 18% and 660% while cell viability was unaffected. Both cell lines formed colonies in soft agar in the absence of butyrate of DMSO, but no colonies were observed in the presence of these agents. However, no differences in in vivo tumorigenicities, when cells were implanted in athymic mice, were seen following treatment. Gross morphological alterations including cell enlargement, process formation, and cellular flattening occurred during culture in butyrate or DMSO. Acrylamide gel electrophoresis in sodium dodecyl sulfate revealed no change in membrane protein constituents, but autoradiographic analysis of membrane glycoproteins demonstrated differences between treated and untreated cells. Ganglioside compositions were altered, and a sialyltransferase required for the synthesis of GM3 ganglioside was elevated by butyrate. Although cytoplasmic aminooligopeptidase remained unaffected by butyrate or DMSO, brush border-associated activity was enhanced by butyrate. Alkaline phosphatase also rose dramiatically during culture in butyrate but was not enhanced by DMSO.