Involvement of T-lymphocytes in the pathogenesis of psoriasis and atopic dermatitis is well established. The question arises as to whether not only tissue infiltrating but also circulating T-lymphocytes are involved in the disease process. Therefore we sought to determine whether T-lymphocytes from patients with psoriasis and atopic dermatitis show abnormal biological behavior to the proinflammatory chemokine interleukin 8 (IL-8) in vitro as studied by their chemotactic activity. In addition, the expression of T-cell activation markers such as HLA-DR and interleukin 2 receptor (IL-2R) were analysed with FACS-technique. In all, 25 patients with psoriasis (13 patients with severe psoriasis and 12 patients with mild psoriasis) and 11 patients with atopic dermatitis were investigated. For comparison. T-lymphocytes from 14 healthy controls were tested equally. The results show that T-cell chemotactic responses to IL-8 were significantly decreased in patients with severe psoriasis as compared to healthy controls. T-cells from patients with atopic dermatitis demonstrated an even more pronounced decrease in chemotactic response as compared to T-cells from psoriasis patients or healthy controls. In contrast, increased expression of activation markers HLA-DR and IL-2R were demonstrated in circulating T-cells from patients with severe psoriasis and atopic dermatitis in comparison to healthy controls. It can be concluded that circulating T-cells in patients with severe psoriasis and atopic dermatitis show a decreased in vitro chemotactic response to IL-8. Furthermore, the in vivo phenotypic activation state of T-lymphocytes in these patients seemed to be associated with their decreased in vitro functional capacity.