The investigations were conducted on 3 groups of New Zealand rabbits: 1) controls; 2) injected with procain, i.m. 15 mg/kg body weight, daily, for 30 days; 3) injected with diethylaminoethanol (DEAE), 15 mg/kg body weight, daily, for 35 days. The study was made also on human leukocytes, isolated from the peripheral blood of 10 clinically healthy subjects (adults), procain and DEAE action being investigated in vitro. The free oxygen radicals (FOR) released by PMN leukocytes were evaluated by chemiluminescence, in vitro. Addition of procain or DEAE had no effect on the release of FOR by PMN leukocytes of control rabbits. In the experiment made on rabbits treated with procain or DEAE, the release of FOR by PMN leukocytes was much more reduced, as compared to controls. In the rabbits treated with procain, the intensity of the emitted light was 2.27 mV, in those treated with DEAE, 3.46 mV, while in the controls, the mean value was 6.74 mV. In the in vitro experiments performed on human PMN cells stimulated with opsonized zymosan (OZ), addition of procain or DEAE had an inhibiting effect on the FOR release. As compared to control, the means of the FOR values decreased from 59 to 41.2 mV in case of procain addition and from 67.7 to 50 mV in case of DEAE addition. The fact that the inflammation is associated with accumulation of free radicals, suggests the opportunity to test these substances, especially DEAE, as antioxidant agents.