The total of the persons examined was divided into 3 groups. There were 11 men and 5 women with various diseases diagnosed in Group I, 5 healthy men in Group II and 9 man and 2 women with allergy in Group III, the control group. The subjects were treated with hyperbaric oxygenation exposures from 1.8 to 2.5 ata O2 within a 60-90 minute period. The number of exposures ranged from 1-4 for Group II till 10-15 for Group I and Group III. In all the cases the following examinations were carried out: hematological tests (Hb, Ht, erythrocytes, leucocytes, and blood platelets counts, blood picture), immunological tests (IgG, IgM, IgA, IgD, IgE, C3 fraction of complement and hematolytical activity of complement--CH50) and all required additional clinical tests. These examinations were made before the series of hyperbaric exposures, after 4 exposures, after their completion and a month later. Full documentation in Group I was obtained in 6 cases and in the 10 remaining only before the exposures and after their completion. In Group II full documentation was available only in 1 person, but before the exposures and after their completion in the rest, and finally, in Group III full documentation was obtained in 7 persons, but before the exposures and after their completion in 4 others. Generally, it was in allergic states that a positive therapeutic effect of hyperbaric oxygenation was found. It had already been corroborated by the respective shifts of immunological coefficients, noted by other authors too. The above observations need to be confirmed in a wider material, in different periods of the disease and with other additional examinations employed.