Homogenates of tissue from the female genital tract contain isoamylases which are, to a certain extent, electrophoretically distinguishable from the pancreatic and salivary isoamylases. In healthy nonpregnant women, high levels of activity of genital isoamylases were found in tissue homogenates of cervical and Fallopian tube mucosa, whereas activity was weak or absent in homogenates of endometrium. The isoamylases of the cervical mucosa had an electrophoretic migration rate toward the anode identical to that of the salivary main fraction, whereas the isoamylases of the Fallopian tube migrated faster. Specific genital isoamylase activities were also demonstrable in peritoneal fluid collected from the cul-de-sac. During the menstrual cycle, these activities showed a midcycle peak. In pregnant women, the levels of activity of the genital isoamylases in peritoneal fluid were lower than in nonpregnant women. In homogenates of the male accessory genital glands, the isoamylases specific for the genital tract were present in minute amounts. The isoamylases specific for the genital tract were not detectable in serum in either sex.