A group of 28 psoriatic patients was examined before a topical treatment and afterwards. Samples of peripheral blood were obtained and analysed in a flow cytometry with respect to subpopulation of lymphocytes with a particular care paid to percentage and expression of CD45RO and CD45RA cells. The received results were compared with those from the group of 22 healthy controls. The study showed that the mean percentage of CD45RO+ cells in the psoriatic patients was significantly higher than in the control group (p < 0.005). In the psoriatic group there were no statistically significant differences between the values of any of the parameters studied before and after the treatment.