Neutralization of negatively charged groups in the glomerular capillary wall by polycations causes extensive loss of podocyte footplates, formation of tight and gap junctions, and dislocation of slit diaphragms within a few minutes (MW Seiler, MA Venkatachalam, and RS Cotran: Science 189: 390, 1975). This study attempts to elucidate further the development of podocyte abnormalities by quantitating the effects of inhibitors of microfilaments, microtubules, and cellular metabolism. The decrease in the number of footplates per micrometer of basement membrane caused by the polycationic chemical protamine sulfate (PS) was determined after in situ perfusion of the left kidney of rats. An approximate 50 per cent amelioration of this effect of PS was observed when in addition to perfusion with PS:(1) perfusion was performed in the cold (6 degrees C.);(2) the perfusate contained cytochalasin B;(3) the perfusate lacked Ca2+; and (4) the perfusate contained ethylenediaminetetraacetic acid. In contrast, colchicine did not affect PS-induced footplate loss. It was concluded that the PS-induced footplate retraction observed in scanning micrographs, is partially an active process involving podocyte actin filaments. Intact microtubuli are obviously not necessary. Formation of tight and gap junctions between foot processes and dislocation of slit diaphragms were not influenced by any of the inhibitory conditions listed above.