Human kidney tumour cells in culture incorporated [3H]glucosamine and 35SO4 into glycoprotein products, which were secreted into the culture medium. The effects of sodium butyrate, a known differentiation-inducing agent, on the production of these sulphated glycoproteins were studied. Cells were cultured in the absence or presence of butyrate (2 mM) in serum-containing medium, for various times, and the labelled glycoproteins were partially purified by DEAE-cellulose chromatography. Treatment of these cells with butyrate resulted in an increase in the synthesis of secreted [3H]glucosamine- and 35SO4-labelled glycoproteins over several days of culture. This same increase in levels of 35SO4 incorporation was not observed with B16 melanoma cells. Sodium dodecyl sulphate (SDS)/polyacrylamide gel electrophoresis revealed that five major glycoproteins labelled with [3H]glucosamine also were labelled with 35SO4. The major secreted glycoproteins from cells cultured in the absence or presence of butyrate over a 3-day period were similar by SDS/polyacrylamide gel electrophoresis. Analyses of Pronase-derived glycopeptides indicated that these secreted 3H/35S-labelled glycoproteins contained sulphated oligosaccharides with terminal sialic acid----Gal----GlcNAc residues similar to glycoproteins secreted by vascular endothelial cells.