Abstract
Extracts of the ovaries of pregnant sows and the blood of pregnant rabbits prepd. for their ability to produce relaxation of the symphysis pubis of the guinea pig were found to possess an antidiuretic action in the rabbit. Control extracts of beef heart and blood of male rabbits prepd. in a similar manner gave negative results. Evidence is presented that the antidiuretic activity parallels the relaxin activity of the prepns. used in the study.