Nineteen weanling pigs were each infected per os with 200 fourth stage Ascaris serum larvae and were fed either a low protein or a high protein diet for 8 weeks. Worms expelled during the 8 weeks were recovered and all worms remaining in the gastrointestinal tract at slaughter were collected. Fifty-four percent of all worms were recovered at slaughter. Ten of the 19 animals maintained an infection for 8 weeks; the other 9 showed no signs of A. suum infection. A total of 377 worms were recovered. Average worm burdens were 37.7 worms per pig, 50.8 worms per low protein pig, and 30.8 worms per high protein pig. Times of and possible causes for expulsion are discussed. Procedure for infection of pigs is discussed in detail and possible improvements in technique are suggested.