Subcutaneous grafts of fresh or freeze-dried hepatic schistosome egg granulomas in inbred mice caused increased numbers of total cells, T cell subsets, and elevated DNA synthesis in regional lymph nodes. This in vivo T cell activation was not apparent by in vitro tests. Spleen cells were unaffected both in vivo and in vitro. Immunosuppressive therapy with ciclosporin or monoclonal antibodies to T cell subsets profoundly depressed the T cell numbers and function, even when primed by a prior graft. Subsequent grafting partly reversed these effects, and T cells became activated. The findings indicate that in vitro assessment of activation and suppression of T cell function does not necessarily correspond to the events occurring in vivo.