Host protective immunity to the intestinal dwelling nematode Trichinella spiralis is mediated by CD4+ mesenteric lymph node (MLN) cells during the course of intestinal infection. The present study has examined the cytokine production by T cells within the MLN of two H-2-compatible strains of mice infected with T. spiralis which differ in the speed at which they expel the parasite from the gut. For both strains of mice, in vitro stimulation of MLN cells with a protective worm antigen preparation resulted in secretion of elevated levels of interleukin-3 (IL-3), IL-4, IL-5 and IL-9 compared to controls. Negligible levels of interferon-gamma (IFN-gamma) were secreted. Furthermore, a similar pattern of cytokine secretion was observed from MLN cells taken from infected mice after in vitro stimulation by T-cell mitogens. No evidence was found for a relationship between quantity of cytokine secreted and the differences in speed of parasite expulsion in the two strains of mice studied. The results support the hypothesis that protective immunity to T. spiralis infection is associated with the activation of Th2-type cells within the MLN in the relative absence of Th1-type cells.