Toxicities in rats with free versus liposomal encapsulated cisplatin. Wistar rats (five in each group) were given either 1 mg/kg of free cisplatin, 1 or 2 mg/kg of liposomal encapsulated cisplatin, or saline solution intraperitoneally biweekly for 15 injections. Rats in the free drug group showed significantly less weight gain; two rats died during the study. At necropsy, the free cisplatin--treated rats showed gross and microscopic evidence of peritoneal fibrosis that was not detected in any of the remaining groups. The free cisplatin--treated rats showed serum and histologic evidence of renal damage; all five rats had moderate or severe acute tubular necrosis. No renal abnormalities were detected in rats that received 1 mg/kg, and only focal or mild changes were found in rats that received 2 mg/kg of the liposomal preparation. Neurotoxicity, as determined by nerve conduction and inclined plane studies, developed in rats treated with free and liposomal cisplatin. These results are encouraging and warrant further investigation. 