Adult T cell leukemia (ATL) cells show a mature helper-inducer T cell phenotype and are thought to secrete many kinds of cytokines in vivo, complicating the clinical features in these patients. In an attempt to specify the cytokines produced by ATL cells, we measured the cytokine concentration in the culture supernatants of three ATL cell lines, all of which were confirmed to be true peripheral blood ATL cell in origin. All these cell lines showed the same cytokine production profile, secreting IL1-alpha, IL1-beta, LD78(MIP-l alpha), TNF-alpha, IFN-gamma, and GM-CSF, but not secreting IL-1 alpha, IL-1 beta, IL-1 receptor antagonist (IL-1 Ra), IL-4, IFN-alpha, and G-CSF irrespective of the stimulatory agents used. Such limited cytokine production may indicate the specific origin of ATL cells within the helper-inducer T cell subtypes. Moreover, these results explain some of the unusual clinical features of ATL patients.