The levels of T-cell activation through classical and alternative pathways were studied in persons participated in cleaning-up operations at Chernobyl N. P. P. Proliferation response of T-cells on the action of monoclonal antibody anti-CD3 (classical activation) as well as response on phytohaemagglutinin was partially decreased just as response on autologic erythrocytes in combination with phorbol 12-myristate-13 acetate (CD2-dependent alternative activation) was completely suppressed in all affected persons. Addition of interleukin 2 did not restore T-cell responses on both anti-CD3 and alternative stimulation. The different degree of decrease of T-cell responses on anti-CD3 and CD2-dependent alternative stimulation is not a result of respective alterations of cell surface CD3 and CD2 expression.