The effects of the differentiation-inducing agent dimethylsulfoxide (DMSO) on the growth and protein composition of murine hepatic tumor cell (BW77-1) cultures were investigated using various concentrations of the polar solvent in the growth medium. A 4-day exposure to DMSO in concentrations of 0.5, 1 and 3% reduced final hepatocyte population density to 63, 43 and 15% of control values, respectively, while the amount of transferrin in the cellular and extracellular compartments increased in a dose-dependent fashion. The biochemical basis for elevated transferrin extractable per 10(6) BW77-1 cells in DMSO-stimulated cultures was due to increases in both the transferrin contribution to total cellular protein and the mean protein content per cell. This stimulation in cellular protein levels was reflected in the incorporation of [3H]-amino acids into cell-associated 10% trichloroacetic acid-insoluble material. Cultures of transformed liver epithelial cells thus appear to respond to in vitro DMSO exposure by increasing their accumulation of a late-stage hepatocyte gene product.