This study dealt with the in vitro immune responses to stimulation with phytohemagglutinin, pokeweed mitogen, concanavalin A, and purified protein derivative in lymphocytes taken from uremic patients before and after hemodialysis and in normal lymphocytes in the presence of plasma from uremic patients before and after hemodialysis and normal AB serum, as well as the influence of the same plasma factors on one-way mixed lymphocyte culture (MLC) responses of uremic/normal and normal/normal lymphocytes. The results obtained show that uremic plasma contains nondialyzable factors that can suppress both uremic normal and normal/normal lymphocyte responses in MLC and that uremic and normal lymphocytes show asynchronic MLC culture kinetics, thus indicating a changed immune status of uremic patients manifested both at the cellular and at the humoral level.