In this paper we investigated the lymphoproliferative and cytotoxic responses of peripheral blood mononuclear cells (PBMC) of patients affected with lymphoproliferative disease of granular lymphocytes of T cell origin to mitogens and antigens. Most patients with lymphoproliferative disease of granular lymphocytes (LDGL) showed a severely impaired PBMC proliferative capacity in response to phytohemagglutinin, anti-CD3 and tetanus toxoid, an impairment that, in the case of anti-CD3 response, appears to be related to a defect of phosphorylation in response to triggering. In contrast, at least 50% of the patients had normal proliferation in response to a mannoprotein fraction purified from Candida albicans. These data suggest that some CD3+ GL from LDGL patients, that usually respond poorly to proliferative stimuli in vitro, can be triggered to perform these functions by candidal antigens.