Lymphocytes were extracted from six biopsy specimens of oral lichen planus. T-lymphocyte lines were expanded in culture with phytohaemagglutinin and interleukin 2, and cloned by limiting dilution. Fifteen T-cell clones were isolated with a probability of clonality of 96.3%. The majority of clones (n=13) expressed the αβ T-cell receptor, and of these, 11 were CD8+ and two were CD4+. Two clones were CD4 and CD8, and expressed the γδ T-cell receptor. The ability of these clones (effectors) to suppress concanavalin-A-stimulated proliferation of autologous lesional T-cell lines (responders) was assessed. Maximum suppressor activity ranged from 17 to 100%. The majority of clones (n=12), including a CD3+ CD4+CD8αβ+ clone, displayed suppressor activity which was proportional to the effector to responder ratio. A CD3+CD4+CD8αβ+ clone and a CD3+CD4CD8γδ+ clone displayed substantial helper activity at higher effector to responder ratios. These results demonstrate differential helper and suppressor activity of T-lymphocyte clones extracted from oral lichen planus lesions. The balance between help and suppression may be a fundamental determinant of immunological activity within the lymphocytic infiltrate of oral lichen planus, and hence may dictate the clinical behaviour of the disease.