Eleven patients with chronic uveitis treated with Cyclosporine were immunized with keyhole limpet hemocyanin (KLH) and tetanus toxoid. Delayed cutaneous hypersensitivity responses, lymphocyte blastogenic responses, and antibody production were compared with those of similarly immunized control individuals. A significant decrease in delayed cutaneous hypersensitivity (P less than 0.001 for KLH and P less than 0.01 for tetanus toxoid) was observed. No significant differences in blastogenic or antibody responses were noted. These findings demonstrate that the majority of the Cyclosporine-treated patients had intact T cell-dependent antigen responses as measured by both proliferative response and antibody production to primary and secondary antigenic challenges but that other immune functions such as delayed cutaneous hypersensitivity are affected by therapeutic doses of systemic Cyclosporine.