Glomerular epithelial cells (GECs) in vitro provide a useful model for the study of the mechanism(s) underlying the nephrotic syndrome of rats induced by the aminonucleoside of puromycin (PAN). Some of the toxicities of PAN are nonspecific, in that the constituent molecules of PAN (adenosine and puromycin) cause similar effects in vitro. These include GEC blebbing and rounding, reduced uptake of precursors of protein (leucine) and glycoprotein (glucosamine) synthesis, and increased permeability of the GEC membrane to adenosine. Some of the effects of PAN are not reproduced by adenosine or puromycin and are inhibited by the simultaneous presence of N6-monomethyl adenosine (MMA), a PAN analog and an in vivo blocker of nephrosis due to PAN. These processes may be related to the nephrotic syndrome and include the loss of adhesion to plastic; a reduction in the incorporation of 14C-glucosamine and 35S-sulfate both into molecules removable from the GEC surface by neuraminidase and into those moieties precipitated from the culture media by TCA; a marked reduction in the "ordering" of the lipids of the rigid GEC membrane, which is possibly dependent upon cell-surface proteins. These morphologic alterations in GECs and in the distribution of negatively charged molecules, which are either secreted or on the cell surface, correlate with observations made in PAN-induced nephrosis in rats in vivo. These include changes in the turnover and the array of sialic acid and heparan sulfate glycoprotein on the GECs and the glomerular basement membrane. The in vitro sensitivity of GECs to PAN and the effects of MMA suggest a role for these cells in in vivo aminonucleoside nephrotoxicity, where alterations in both the morphology and the anionic topology of GECs participate in the development of proteinuria.