The involvement of superantigens in the pathology of cutaneous T-cell lymphomas (CTCL) has been suggested before, but without unequivocal evidence for superantigen activity in the patients. Seeking evidence for superantigen activity we analysed clones and microdissected single cells isolated from the epidermis of early-stage lesions of a CTCL patient for their T-cell receptor (TCR) V beta expression and TCR V gamma gene rearrangements. The vast majority of these T cells expressed the TCR V beta family type of the tumour. From their TCR gamma gene rearrangements, however, these cells were polyclonal. The tumour cell clone accounted for about 60% of these cells, about 40% were of heterogeneous origin. This dominance of a single V beta family in the polyclonally expanded dermal T-cell populations implies superantigen activity in the CTCL lesions.