The C3 cleavages of human blood kept at different temperatures in vitro were studied. In 14 autopsy cases, the postmortem intervals(PMI) were estimated based on the C3 cleavage rates and the rectal temperatures. The 95% confidence of predicting PMI was?11 hours. The phenotyping of C3 could be achieved while the C3 cleavage rate was measured. It is suggested that it is useful for the personal identification of unknown corpses.

The distribution of C_3 phenotype frequencies in the Han population in Cheng-du area was studied by means of cellulose acetate electrophoresis followed byimmunofixation.In 400 unrelated healthy individuals three C_3 phenotypes weredemonstrated.Their frequencies were as follows:SS=397,FS=2 and SSvar=1.Their gene frequencies were as follows:C_3~S=0.9963,C_3~F=0.0025 and C_3~(svar)=0.0013.The C_3 phenotype frequencies were in good agreement with those expec-ted.C_3 phenotyping in the huma bloodstains kept at 37℃ and room temp-lasserature for two days,at 4℃ for 23 days(cotton bloodstains)and for 35 days(g-bloodstains),and -20℃ for at least 87 days could be performed.C_3 ph-enotypingin human serum could be performed at roon temperature for 3 days,as 4℃ for 13days and at -20℃ for at least 106 days.C_3 phenotyping was usedin five casesof paternity dispute.