Summary Hepatosplenic γδ T cell lymphoma (HSTCL) has been observed in patients with Crohn's disease (CD) who received anti-tumour necrosis factor (TNF)-α agents and thiopurines, but only one case was reported in a psoriasis patient worldwide. This difference could be due to differences in either the nature of the inflammatory diseases or in the use of immunomodulators. We investigated the impact of anti-TNF-α agents on the level and repertoire of γδ T cells in peripheral blood from psoriasis patients. Forty-five men and 10 women who were treated with anti-TNF-α agents for psoriasis were monitored for a median 11 months for the level and clonality of γδ T cells via flow cytometry and polymerase chain reaction (PCR) analysis of T cell receptor gamma (TCR-γ) gene rearrangements. Seventeen men had a repeated analysis within 48 h of the infliximab infusion to reveal a possible expansion of γδ T cells, as observed previously in CD patients. Ten psoriasis patients who were never exposed to biologicals and 20 healthy individuals served as controls. In the majority of psoriasis patients, the level and clonal pattern of γδ T cells was remarkably stable during infliximab treatment. A single male patient repeatedly experienced a significant increase in the level of γδ T cells after infliximab infusions. A monoclonal γδ T cell repertoire in a polyclonal background tended to be more frequent in anti-TNF-α-treated patients than naive patients, suggesting that anti-TNF-α therapy may promote the clonal selection of γδ T cells in psoriasis patients.