The aim of this study was to examine whether there was an increase of suppressor T cells, relative to helper T cells, in the intestinal lamina propria of Hymenolepis diminuta-infected rats, a condition which might allow the parasite to survive for the life-span of the host. Lamina propria cells were isolated by enzymatic procedure. All lymphocytes were passed over nylon wool columns in order to remove B cells; then the T cells were purified by a panning technique using monoclonal anti-T cell antibodies. Changes in the mitogen-stimulated synthesis of 1gM, IgG and IgA by normal peripheral blood indicator lymphocytes, as measured by sandwich ELISA, was used as an index of help and/or suppression. No significant suppressor T cell activity was observed in the cultures, either from control or infected intestine.