The percentage of human granulocytes expressing the integrins CD11b and CD11c as well as complement receptor 1 (CD35) was increased by short-term incubation of whole blood with interleukin-2 (IL-2), interleukin-4 (IL-4) and tumour necrosis factors alpha and beta (TNF-alpha and TNF-beta). The mean fluorescence intensity of granulocyte CD18 was also increased by the above cytokines, whilst that of CD11b was only increased by TNF-alpha. Up-regulation of granulocyte CD18 expression was seen with 1 U/ml of IL-2, TNF-alpha or TNF-beta, in contrast to the effect of IL-4 which was only observed with 100 U/ml. Similarly, enhanced expression of CD35 was induced by 1 U/ml of IL-2 or TNF-alpha but not by concentrations of IL-4 or TNF-beta lower than 100 U/ml. Cytokine effects on the CD11/CD18 complex and CD35 molecules were not modified by cycloheximide, suggesting that their increased expression was not due simply to synthesis de novo. None of the granulocyte surface determinants investigated was altered upon short-term incubation of blood with either IL-1, IL-6 or interferon-gamma (IFN-gamma). The demonstration in vitro that cytokines selectively up-regulate granulocyte integrins and complement receptor 1, suggests that similar mechanisms may be operating during the control of granulocyte-mediated inflammatory processes.