In one experiment, 21 calves were given daily oral immunizing inoculations of 1,000 infective larvae (L3) of Trichostrongylus axei, an abomasal nematode parasites, for 35 weeks. Calves were euthanatized in groups of three every 5 weeks to determine infection kinetics. Worm populations steadily increased through week 30, but the percentage of total inoculum that became established was about the same through week 30. At week 35, the number of worms dropped markedly. In a second experiment, 27 calves given daily oral inoculations of infective larvae were allotted to three groups comprised of three subgroups each: (A), challenge-exposed vaccinated; (B), nonchallenge-exposed vaccinated; and (C), challenge-exposed nonvaccinated. Calves of subgroups A and C were given single challenge inoculums of 200,000 L3 after the 10th, 20th, and 30th weeks. All calves were necropsied 35 days after challenge exposure. When immunity was determined from the equation: [(No. of worms in [(B + C)-A])/No. of worms in [B + C])] X 100, immunity was 35% at 10 weeks, 52% at 20 weeks, and 100% at 30 weeks.