The authors evaluate T-lymphocytes and their sub-populations, the immunoregulating index and white cell haemogram in patients in different clinical stages of HIV infection. They discuss the importance of the investigated parameters, in particular the number of CD4+ T-lymphocytes in the peripheral blood stream as a laboratory criterium for the development of the disease. From the paper ensues that evaluation of the number of CD4+ T-lymphocytes in the peripheral blood stream can help to estimate the time of the primary infection and the selection of an optimal time for starting azidothymidine therapy, but alone it does not suffice for establishment of the prognosis of the development of the HIV infection.