The research took place in Japan. Mixed bloodstains were made on surgical blades and a cedar board. The blades were dipped into of one sample of blood and then dipped into blood of a different group at intervals of 30, 20, 15, 10, and 5 seconds. Two drops of blood were dropped on a cedar board; two drops of a different group were dropped there at the same intervals. The bloodstains dried for a week. The blood samples were removed from the blades or the cedar board and processed with a routine histological method. Three serial thin sections were obtained. The sections were deparaffinized and treated in papain solution for 2 hours at 36 degrees centigrade to unmask antigenic sites on red cell membranes. The research used the LSAB and PAP methods to detect A and B antigens and an indirect immunocytochemical method for H antigen. Results of these methods revealed specific immunologic reactions and allowed determination of the blood group of each blood of mixed bloodstains. Furthermore, these methods indicated the possibility of determining who was stabbed first in situations in which a single knife stabbed two or more victims. Figures, table, and 8 references (Author abstract modified)