To study the clinical manifestations of CNS lesions in HIV patients, to analyze relationships between the conditions of the immune system, the rate of HIV replication, and the clinical picture. Study groups included 128 HIV patients, which had blood CD4 cell counts below 350 L^-1 and were eligible for antiretroviral therapy, 65 patients (Group 1) having no clinical manifestation of CNS involvement, and 63 patients having such manifestations. HIV viral loads in blood plasma and in the cerebrospinal fluid, and the features of blood lesions were determined. In 28,6% of cases, the lesions were associated with mixed infections. In Group 2, HIV viral load in the CSF was 13,2 times higher than in Group 1. In the blood, viral load was significantly higher than in the CSF. It is concluded that tests for HIV as well as and for agents of opportunistic infections in the CSF should be performed in patients with pronounced immunosuppression.