1. The potencies of several neurohypophysial hormones were examined at different times during the oviposition cycle in an in vitro fowl oxytocic assay. 2. Uterine tissues were removed 2 h before (-2h-OP), immediately after (0h-OP) and 5 h after (+5h-OP) spontaneous oviposition. In addition, uterine tissue was removed immediately after oviposition was induced, by administering prostaglandin E2 2 h before an expected oviposition (Induced-OP). 3. The rank order of oxytocic potencies for the peptides was arginine vasotocin = vasopressin greater than oxytocin greater than mesotocin. The sensitivity of the uterus to the hormones was 0h-OP = Induced-OP greater than -2h-OP = +5-OP. 4. These results suggest that uterine sensitivity to neurohypophysial hormones changes during the oviposition cycle in domestic fowls.