The amylo-1,6-glucosidase activity of human seminal plasma was studied using its specific substrate, α-glucosyl Schardinger dextrin. The enzyme activity of semen is predominantly associated with the seminal plasma and proceeds at maximum velocity at pH 5·8 to 6·0. The secretions of seminal vesicles and testis seem to contribute most of the enzyme activity to the seminal plasma. Amylo-1,6-glucosidase activity is significantly lower in azoospermic samples as compared to those with a good sperm count.