A. and OYA, M. Polymorphism of ACPI by Isoelectric Focusing : Population Study in Japanese and Phenotyping in Bloodstains. Tohoku J. exp. Med., 1987, 151(3), 317-321 The polymorphism of ACP1 was investigated in 749 unrelated Japanese individuals by isoelectric focusing. The allele frequencies were A CPl *A =0.2083 and ACPI * B = 0.7917, which were almost similar to those reported in other Japanese subpopulations. The isoelectric focusing technique was successfully applied to ACPI typing in bloodstains ; each phenotype was demonstrated at 37°C for up to 4 weeks, at room temperature for up to 10 weeks and at 4°C for over 16 weeks after stain formation. The isoelectric focusing method proved more useful than conventional electrophoretic methods in medicolegal practice. enzyme polymorphism ; isoelectric focusing ; ACP1 types ; population study in Japanese ; grouping of bloodstains Since the discovery of ACP1 polymorphism by Hopkinson et al. (1963), a large number of works have been performed using starch, agarose or cellulose acetate electrophoresis, and this system is now an accepted genetic marker for paternity testing and blood individualization.Recently, isoelectric focusing has been introduced for the analysis of ACP1 isoenzymes because of the high resolution capacity