A retrospective study over a 3-year period was done looking at predialysis platelet levels, in particular, thrombocytopenia. Seventy-five patients with acute renal failure (ARF) and 75 patients with chronic renal failure (CRF), treated at King Edward VIII Hospital, were randomly chosen. Platelet counts were performed on a coulter counter (S + 2) and counts of less than 150 x 10(9)/L were considered as thrombocytopenia. Of the 75 CRF patients, 47 were males. Eleven (14.7%) were thrombocytopenic with a mean platelet count of 118.3 x 10(9)/L and a range of 83-146 x 10(9)/L. The mean creatinine level was 1510 micrograms/L. The remaining nonthrombocytopenic patients had a mean platelet count of 268 x 10(9)/L and a mean creatinine of 1080 micrograms/L. Of the ARF patients, 39 were males. Twenty-two (29.3%) had thrombocytopenia with a mean platelet count of 98 x 10(9)/L and a range of 22-147 x 10(9)/L. The mean creatinine level was 819 micrograms/L. The remaining nonthrombocytopenic patients had a mean platelet count of 319 x 10(9)/L and a mean creatinine of 1020 micrograms/L. In CRF patients no correlation was found between thrombocytopenia and the disease process. Creatinine levels appear to be higher in the thrombocytopenia group than in the nonthrombocytopenic group. In the ARF group of patients, females had a higher frequency of thrombocytopenia than males. Obstetrical and gynecological causes and herbal ingestion were the 2 major underlying etiologies in the thrombocytopenic group. Thrombocytopenia appears to be a common presenting feature in ARF as opposed to CRF, and this may be accounted for by the underlying etiologies in ARF.