Changes in the integrity, ultrastructure, phagocytosis capacity, and production of H 2 O 2 , O ÁÀ 2 and NO À 2 were evaluated in cultured neutrophils. The activities of the antioxidant enzymes (catalase Ð CAT, superoxide dismutase Ð SOD and glutathione-dependent peroxidase Ð GSH-Px) were measured under similar conditions. The integrity of the cells remained unchanged up to 18 h. After 24 h, the number of viable cells in culture dropped by 16 per cent. The percentage of viable cells in culture was of 72 per cent even after 72 h. An ultrastructural analysis of the cells was carried out after 3, 6, 12, 24, 48, and 72 h in culture. Neutrophils started developing morphologic changes after 24 h: decreased cell volume, abundant vacuoles (mainly around the nucleus), and also the presence of autophagic vacuoles. This period was then chosen for the study of neutrophil function and antioxidant enzyme activities. Neutrophils cultured for 24 h presented reduced phagocytosis capacity. The rates of production of H 2 O 2 and O ÁÀ 2 remained unchanged after 24 h in culture. Concomitantly, these cells were also able to produce NO in signi®cant amounts. The production of O ÁÀ 2 in response to PMA stimulus was lowered in 24-h cultured cells. Possibly, the production of oxygen and nitrogen reactive species accomplished with a decrease in the activities of CAT and GSH-Px play a key role for the process of apoptosis which takes place in neutrophils under these conditions.