This study investigated . in-vivo cell-mediated immune (CMI) responses in elite swimmers over a 5-month training season, to assess the impact of intense training on changes in T-lymphocyte function. The CMI Multitest™ was performed early in the season after a period of rest, during peak high-intensity training, and late in the season during the precompetition taper period. The CMI tests were performed at rest prior to a morning training session. There were no significant differences between the swimmers and a control group for any of the seven CMI antigen responses at any of the test points during the season. In the swimmers, there were no significant differences in the number of positive responses to the CMI antigens between the three test points (Friedman's test=9.6364, p=0.47) and no significant differences for the CMI cumulative scores (Friedman's test = 11.98, p=0.29) at each test point. There was no consistent pattern for changes in CMI cumulative scores for individual swimmers over the training season. The findings of this study indicate that, despite reported transient T-lymphocyte immune suppression immediately after intense exercise, probably associated with acute redistribution and temporary pooling of blood T cell subsets in extremities, the T-lymphocyte function involved in CMI responses is not compromised by extended periods of training at an elite level.