Coronavirus infection (CVI) was studied in 227 patients hospitalized in the clinic of the Research Institute of Hematology and Transfusiology in 1993-2003 with diagnosed acute and chronic leucosis, multiple myelogenic disease and aplastic anemia. Their blood sera and secretions of the nasal cavity were examined in the indirect hemagglutination (IHA) test with dried standard erythrocyte diagnostic preparations. CVI was shown to be activated in three year cycles in immunodeficient patients, which occurred, respectively, in 66.1, 56.9, 47.8 and 51.6% of cases in the above mentioned groups of patients. In 87% of cases CVI was associated with other respiratory pathogens, the following being prevailed: respiratory syncytial virus (37.9%), parainfluenza virus (32.2%) and Mycoplasma pneumoniae (36.8%). CVI was provoked by such factors as the course of the main disease and specific treatment, previous respiratory infections of other etiology with M. pneumoniae infection playing the leading role (60%). The most severe course of CVI was observed in patients with acute leucosis (in 75% of cases accompanied by lesions of lower respiratory tracts). The use of the highly sensitive IHA test made it possible to determine the potential for both serum and local antibodies production in the patients under observation.