1. A method is described for the isolation of rat platelets. The method gives high yields of platelets with negligible white and red cell contamination.
2. Rat platelets were labeled in vivo with radioactive diisopropylfluorophosphate (DFP32). The platelet life span was the same in normal, splenectomized and hypersplenic rats.
3. Some problems involved in the use of DFP32 as a blood cell label are discussed.