Adult Mansonella perstans infected the abdominal cavity of nine patients seen at Karawa Hospital in the Ubangi territory of Zaire. In four patients the worms were removed at laparotomy, and in the other five they were removed at autopsy. Twelve adult worms were identified in the nine patients. None of the worms caused symptoms or contributed to the patient's death. Worms were in the hernial sac in three patients, and one each was in connective tissue beside a reactive mesenteric lymph node, in peripancreatic connective tissue, in perirenal connective tissue, in hepatic portal connective tissue, on the serosal surface of the small intestine, and in connective tissue adjacent to rectum. The diameter of male worms was 45 microns to 60 microns and of female worms, 80 microns to 125 microns. One female worm was removed intact. It was 6 cm long and had a bifurcated tail characteristic of M. perstans.