Experiments were carried out with mice of CFW inbred strain infected with 200 Trichinella spiralis larvae and divided into two groups: experimental and control. The experimental mice were injected with phytohaemagglutinin P (PHA-P), 24 h before infection. The all animals were killed between 7-133 days post infection and the pieces of spleens, mesenteric lymph nodes, jejunum and masseter muscles were sectioned in a cryostat and examined with monoclonal antibodies (anti-Thy 1, 2, anti-CD4+ and anti-CD8+) by immunoenzymatic method. In the animals treated with PHA-P, more numerous CD4+ cells were observed in comparison with the control. The CD8+ cells were stimulated only in the muscles. The most important problem were the CD4+ and CD8+ cells inside the larvae capsules. The role of the CD4+ and CD8+ cells in the immunopathological changes in the course of trichinellosis was discussed.