Activity of cAMP phosphodiesterase was similar in leukocytes of healthy persons and of the patients with bronchial asthma in the period of remission. The enzymatic activity was independent on the form of the impairment (infectious-allergic or atopic types). Sensivity of cAMP phosphodiesterase to the effect of its inhibitors and stimulants--theophylline, papaverine and imidazole was higher in the patients as compared with the healthy persons. Prolonged therapy with the phosphodiesterase inhibitors did not lead to development of resistance.