Mononuclear phagocyte-derived cytokines are important regulators of haemopoiesis in inflammatory conditions. By means of radioimmunoassay we measured the levels of two cytokines, tumour necrosis factor-alpha and interleukin 1 beta in sera from subjects infected with human immunodeficiency virus, and related the levels to the presence and severity of haematological abnormalities. The levels of tumour necrosis factor-alpha were significantly higher in patients with anaemia (142 +/- 17 (SE) pg ml-1), lymphopenia (107 +/- 20 pg ml-1) or both (137 +/- 21 pg ml-1) than in individuals without anaemia (18 +/- 5 pg ml-1; P less than 0.001), without lymphopenia (16 +/- 7 pg ml-1; P less than 0.001) or without either disorder (19 +/- 7 pg ml-1; P less than 0.001). A strong negative correlation was found between tumour necrosis factor-alpha and haemoglobin values (r = -0.83, P less than 0.001) and absolute lymphocyte count (r = -0.66, P less than 0.001) in human immunodeficiency virus infection. The changes in the levels of serum interleukin 1 beta were less pronounced but followed the same general trend as the changes in tumour necrosis factor-alpha. The results show that the production of mononuclear phagocyte-derived cytokines is enhanced in acquired immunodeficiency syndrome, and that the levels of these factors are correlated with the presence of certain haematological abnormalities.