In 1934 Selye reported that lactation was inhibited if the uterus of the rat was distended with paraffin on the day the litter was born. It was also stated that involution of the mammary glands was evident as early as 4 days after the operation. Attempts to utilize this method of suppression of lactation have indicated that factors other than the distention of the uterus are responsible if lactation is suppressed. When the wt. loss of the mother rat does not exceed 20 gs. in the first 2 days after the operation and the wt. becomes stabilized there has been no inhibition of lactation. The traumatized mother rat does not allow the young rats to suckle during the first 24 hrs. after the operation. The initial starvation of the litter may be avoided by using a normal foster mother for this 24 hr. period and then returning them to their paraffin injected mother. Mother rats whose uteri were distended with a total of 17 to 20 cc. of paraffin have uniformly demonstrated their ability to rear 6 to 8 young at a normal growth rate. Data will be presented to show that mechanical distention of the uterus does not interfere with the hormonal control of lactation.