Seventeen bitches with pyometra or postpartum endometritis were treated with prostaglandin F2 alpha. Response to the treatment included cessation of uterine discharge, decrease in uterine diameter, reduction in plasma progesterone concentration, and return of a normal leukogram. Treatment of 14 bitches was successful, and 13 of these bitches subsequently experienced estrus. Of those 13 bitches, 11 were bred and 9 became pregnant. In 2 bitches, pyometra developed again, within 6 weeks of the following estrus, illustrating that bitches so affected are susceptible to recurrence of the disease. Of 4 bitches with closed cervix, one failed to respond to treatment, and two bitches with closed cervix required ovariohysterectomy shortly after instituting treatment.