A total of 286 rats were involved in an experiment, with 123 of them being control and 153 receiving daily injections of hydrocortisone (H) in a dose of 3 mg per 100 g body weight. Ten rats were intact. With regard to CNS changes 2 periods were identified in H-treated rats with experimental brain abscess and leptomeningitis: the first was characterized by the effect of the hormone at the acute period of the disease (3-7 days), the second by its action following the long-term administration (15-30 days). In the first 7 days, by reducing the inflammatory reaction, water-electrolyte disturbances and the activity of acid and alkaline phosphatases in the cerebral tissue, as well as by increasing the RNA synthesis in neurons, H prevented the dissemination of the process into the surrounding tissue, swelling and edema, expedited wound clearance and helped to reduce the mortality rate. The use of H for 10-30 days led to the tigrolysis of neurons, elevation in the activity of acid and alkaline phosphatases and brain edema, as well as to a reduction in DNA levels in neurons and a dramatic rise in the mortality rate. The findings indicate the advisability of H utilization in the treatment of brain abscess and leptomeningitis only in the acute period of the disease and as a short course.