THE PREPARATION OF BLOOD AND SEMEN SAMPLES FOR ANALYSIS, THE ASSAYS USED FOR VARIOUS MARKER ENZYMES AND PROTEINS, AND THE RESULTS OF THESE ASSAYS ARE PRESENTED IN DETAIL. LABORATORY DATA SHOW THAT PHOSPHOGLUCOMUTASE, PEPTIDASE A, AND PHOSPHOGLUCOSE ISOMERASE ALL ARE PRESENT IN SEMEN AT LEVELS SUBSTANTIALLY HIGHER THAN THEIR MINIMUM QUANTITATIVE TYPING LIMIT LEVELS. THEREFORE, THERE IS NO MAJOR QUANTITATIVE BARRIER TO THEIR ANALYSIS. PHOSPHOGLUCOMUTASE HAS THE GREATEST POTENTIAL VALUE BECAUSE IT IS NOT DIFFICULT TO TYPE IN DRIED AND LIQUID SEMEN AS LONG AS THE LABORATORY TECHNICIAN IS AWARE THAT ITS PHENOTYPIC EXPRESSION IN SEMEN IS SOMEWHAT DIFFERENT FROM THAT IN BLOOD. PEPTIDASE A IS OF VALUE ONLY IN SITUATIONS INVOLVING BLACK MALES, WHILE PHOSPHOGLUCOSE ISOMERASE IS FOUND IN ONLY 1 PERCENT OF THE POPULATION AND IS OF EXTREMELY LIMITED VALUE. THOSE PROTEINS WHICH HAVE MODERATE ACTIVITY AND CAN BE TYPED UNDER FAVORABLE CIRCUMSTANCES ARE ADENYLATE KINASE, AMYLASE, ESTERASE D, GLYOXALASE, GLUCOSE-6-PHOSPHATE DEHYDROGENASE, 6-PHOSPHOGLUCONATE DEHYDROGENASE, AND TRANSFERRIN. THE USEFULNESS OF THESE SUBSTANCES IS DISCUSSED. THE MARGINALLY USEFUL MARKERS ARE ALSO IDENTIFIED. OF THESE THE IMMUNOGLOBULIN MARKERS ARE THE MOST POTENTIALLY USEFUL BUT THEIR TYPING REQUIRES EXPERTISE AND REAGENTS NOT COMMONLY AVAILABLE IN FORENSIC LABORATORIES. TABLES AND FIGURES ILLUSTRATE THE LABORATORY DATA. PROCEDURES FOR DETERMINING POLYMORPHIC PROTEIN LEVELS IN BOTH BLOOD AND SEMEN ARE DISCUSSED. THE POTENTIAL FOR EVIDENCE ANALYSIS IS EVALUATED. REFERENCES ARE PROVIDED. (GLR)