We examined the role of reactive oxygen species (ROS) in puromycin aminonucleoside (PAN)-induced changes to glomerular epithelial cells (GECs) in vitro. Levels of superoxide anion (O2.-), hydrogen peroxide (H2O2) and hydroxyl radical (HO.) were measured in rat kidney-slice cultures containing PAN with or without antioxidants (allopurinol, probucol and alpha-tocopherol/ascorbic acid). GEC morphology was assessed after three days of culture using transmission (TEM) and scanning (SEM) electron microscopy. The effects of hypoxanthine on GEC ultrastructure was also assessed. O2.-, H2O2 and HO. were generated when PAN was added to kidney-slice cultures in Medium 199. TEM morphometry revealed that incubation with PAN (100 micrograms/ml) significantly (P < 0.05 at least) retarded the loss of GEC foot processes normally seen in vitro. When the hydrophobic antioxidants probucol or alpha-tocopherol/ascorbic acid, which scavenged/inhibited generation of O2.-, H2O2 and HO., were added to cultures containing PAN, the effect of PAN on foot processes was abolished. The TEM appearance of GECs now resembled that seen in control cultures. On the other hand, SEM revealed that probucol and alpha-tocopherol/ascorbic acid provided no protection against the changes induced by PAN in GEC cell bodies or major processes. Allopurinol provided no protection against the changes induced by PAN in GEC cell bodies, major processes or foot processes. The addition of hypoxanthine to kidney-slice cultures did not result in the generation of O2.-, H2O2 or HO., or alter GEC ultrastructure. These findings indicate that ROS play a role in PAN-induced alterations to GEC foot process architecture in vitro. However, the xanthine oxidase pathway does not appear to play a major role in generating ROS from PAN in vitro.