Adoptive transfer of immunity against the enteral phase of Strongyloides ratti was monitored using four parameters; namely, number of worms recovered, position occupied in the host's small intestine, worm length and fecundity. When immune mesenteric lymph node cells (IMLNC) were transferred from donors infected for 20, 26 or 32 days into recipients infected for 3 days, a marked acceleration of worm expulsion was evident by day 16 post-infection (p.i.). IMLNC from day-16 p.i. donors did not transfer expulsion. In an experiment in which recipients were given 2 x 10(8) or 1 x 10(8) IMLNC from donors infected for 26 days, accelerated worm expulsion occurred only with the higher inoculum, although manifestations of direct worm immunity, i.e. altered position and reduced length and fecundity, were evident in both cases. Transfer of IMLNC appeared to have no effect upon worm establishment; when cells were transferred on the day of infection a period of 16 days was necessary to effect both direct anti-worm immunity and expulsion, although the former was evident on day 14 p.i. However, when IMLNC were transferred to rats already infected for 6 days, a very significant reduction of their worm burden was apparent 10 days after IMLNC transfer.