1. Renal localization of autologous 111 In-labelled platelets was studied in patients with chronic glomerulonephritis. External imaging was performed with a γ-camera fitted with a medium energy collimator and the images were collected by a computer. 2. Images of 111 In-labelled platelet distribution showed that there was a marked contribution to the radioactivity within each renal silhouette from adjacent spleen or liver. It was not possible to demonstrate renal accumulation of 111 In-labelled platelets. 3. The application of 111 In-labelled platelets to the study of intrarenal platelet consumption in chronic glomerulonephritis is limited by the sensitivity of current techniques and the scatter from adjacent splenic and hepatic radioactivity.