The macrolide, FK-506, is a potent and effective inhibitor of lymphocyte activation. We studied the effects of FK-506 on human neutrophil activation induced by chemoattractants and by various substances which circumvent receptor stimulation. After preincubation for 5 min at 37 degrees C, FK-506 (1 microM) inhibited N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe)- or platelet-activating factor-induced superoxide production in neutrophils by about 30%. At therapeutic concentrations (0.1-1 nM) FK-506 was ineffective. FK-506 did not inhibit exocytosis and rises in cytosolic Ca2+ concentration [Ca2+]i mediated by these stimuli, and it did not at all inhibit neutrophil activation induced by C5a, leukotriene B4 and 4 beta-phorbol 12-myristate 13-acetate. FK-506 (1 microM) inhibited A23187-induced exocytosis by about 35%, but A23187-induced superoxide production was unaffected. After preincubation for 5 min at 37 degrees C, FK-506 inhibited fMet-Leu-Phe-induced superoxide production in dibutyryl cAMP-differentiated HL-60 cells by about 20%; preincubation with the drug for 24 h did not result in inhibition of superoxide production. FK-506 did not inhibit agonist-binding to formyl peptide receptors and fMet-Leu-Phe-stimulated GTP hydrolysis of heterotrimeric regulatory guanine nucleotide-binding proteins (G-proteins) in membranes from dibutyryl cAMP-differentiated HL-60 cells. FK-506 did not change steady-state and differential polarized phase fluorescence in HL-60 membranes using 1,6-diphenylhexa-1,3,5-triene and 12-(9-anthroyloxy)-stearate as probes. Our results show that FK-506 at supratherapeutic concentrations partially inhibits neutrophil activation. Inhibition by FK-506 of fMet-Leu-Phe-induced superoxide production is rapid in onset and is not due to inhibition of agonist-binding to receptors, interference with G-proteins or protein kinase C, reduction of rises in [Ca2+]i or alteration in physical membrane state.