Piglets in age groups four, eight, 12, 16 and 20 weeks were inoculated with M. avium sereotype 4. A control group of pigs of the same age was also kept. These were not infected. The two groups were kept apart for four weeks and then allowed to mingle. Blood samples were taken from both groups at regular intervals and the animals received the intradermal skin test for TB. The pigs were slaughtered at market weight (about 230 pounds). At time of slaughter blood was drawn for an ELISA test.