Many things are still not clear in the etiopathogenesis of psoriasis. Health workers in various branches of medicine and even those working in other professions linked with medicine can contribute to gaining more knowledge about its etiology, pathogenesis, diagnosis or treatment. This work presents results from observations of 19 patients with a severe form of psoriasis. Material for immunohistopathological examinations was taken from the margins of chronic psoriatic sites twice from each patient: before treatment and after a 4-week treatment by cyclosporin A. Numeric value of CD4+ T lymphocytes, CD8+ T lymphocytes, their ratios and the values of PASI score were followed. Significant decrease in CD4 T lymphocytes and slight decrease in CD8+ T lymphocytes where observed after treatment. The CD4+:CD8+ ratio dropped from the values of 2.10 to 1.68. A dramatic decrease in PASI score was observed--from the average value of 23.34 to the average value of 11.97. The authors compare and discuss the results of similar cytophotometric studies found in the works of other researchers, but this type of results (CD4+ and CD8+ T lymphocytes subpopulations) is very rare in available literature. The decreases found in all studied parametres correspond with clinically well-known treatment effect of cyclosporin A whose immunomodulating effect is targeted mainly at the T lymphocyte inflammatory population.