Recent studies of the cytokine pattern in skin lesions of patients with cutaneous T-cell lymphoma (CTCL) have shown that interleukin-4 (IL-4) and Il-10, both cytokines produced by T-helper type 2 cells, dominate in these lesions. Also, in single studies, interferon-gamma (IFN-gamma), a major cytokine of Th-1-cells, has been found to be absent. Consequently, it has been hypothesized that immune-suppressive Th-2 cytokines may promote local growth of the malignant lymphocyte clone. However, there is so far no evidence for T-cells as the source of the Th-2 cytokines in CTCL skin lesions nor have these cytokines been investigated at a clonal T-cell level. We established a total of 120 T-cell clones (TCCs) from lesional skin and 54 TCCs from the blood of four patients with mycosis fungoides. Epidermal TCCs (mostly CD8-positive) and dermal TCCs (mostly CD4-positive) were stimulated by the mitogen concanavalin A and, seeking a polarized cytokine pattern, the supernatants were assessed by ELISA. We showed that the vast majority of TCCs were able to secrete IFN-gamma and IL-4. IFN-gamma-deficient TCCs occurred only in the epidermis. Some (18) TCCs were found to be either negative for IL-10 production or to produce low levels only. No significant differences were observed between blood- and skin-derived TCCs. Thus a polarized Th-2 cytokine pattern was not detectable among cultured skin-infiltrating nonmalignant T-cells (TILs) isolated from early mycosis fungoides. It therefore appears unlikely that Th-2-mediated immune suppression is a major mechanism operating in early CTCL. However, this does not exclude its role in late-stage disease.