Since PI shows considerable genetic variability, the detection of PI types is routinely used for the forensic examination of blood in paternity and individualization tests. A relatively high content of PI in semen has been recorded, although the origins, biochemical properties, and biological functions of seminal PI are unclear. Before this system can be used for the typing of semen, it is necessary to confirm that the types of PI in semen display the same characteristics as those in blood. This study reports the results of a trial to determine the seminal PI content and the correlation between the PI types in blood and semen samples from the same individuals. The blood plasma and semen samples used in this study were collected from 48 healthy Japanese male volunteers. Five common PI types (M1, M1M2, M1M3, M2, and M2M3) were detected in the blood plasma samples; however, PI-specific bands in semen migrated more cathodally than those in plasma into a PI region of approximately 5.05, and approximately 17 percent of the semen samples could not be phenotyped; the rest were easily phenotyped, and their PI types were found to correlate with the type found in the corresponding blood samples. PI typing could, therefore, provide an additional discriminant characteristic for the forensic examination of individualization from semen samples. 2 figures and 24 references