The immunopharmacologic effects of Isoprinosine (INPX) have been associated with clinical benefit to the patient in a number of conditions characterized by immunodeficiency of diverse etiology. Immunodepressed homosexuals at risk of developing acquired immunodeficiency syndrome (AIDS) treated with placebo or INPX experienced an increase in the function and number of immunocompetent cells associated with clinical improvement. A multicenter trial designed to confirm these results has demonstrated that INPX produced an increase in natural killer (NK)-cell activity, total T cells, and T-helper cells, with certain effects persisting for months after completion of the 28-day treatment period. INPX-treated patients also experienced clinical improvement and decreased incidence of progression to AIDS. The administration of INPX for longer periods to patients with frank AIDS under a compassionate-use protocol has also proved useful. Clinical benefit associated with INPX treatment has been demonstrated in other patients with a depressed immune response, such as aged patients, cancer patients, severely burned patients, ill patients, and surgery patients. This program of clinical trials supports the therapeutic use of INPX in the treatment of AIDS and other acquired immunodeficiencies of clinical importance.