Human polymorphonuclear leukocytes (PMNL) were incubated for 60 min at 37 degrees C with 20 microM or 100 microM prednisolone, and stimulated thereafter for 1 min with 10 nM LTB4, 10 nM LTC4, 10 nM LTD4 or 10 microM histamine. The amount of thromboxane B2 (TXB2) formed by PMNLs was measured by radioimmunoassay. PMNLs spontaneously released TXB2 during 60 min incubation, and the rate of formation was significantly reduced in the presence of 20 microM or 100 microM prednisolone. LTB4, LTC4, LTD4, and histamine stimulated the rate of TXB2 production during 1 min incubation to 93-, 49-, 60-, and 55-fold, respectively. Preincubation with prednisolone for 60 min had a slight inhibitory effect on the stimulated TXB2 formation but TXB2 production still remained many fold as compared to its spontaneous rate of formation. The present study indicates that human PMNLs are capable of synthetizing TXB2, and its spontaneous rate of formation is inhibited by a synthetic glucocorticoid, prednisolone. The great stimulatory effect of LTB4, LTC4, LTD4, and histamine suggests that these agents may activate phospholipases or other acylhydrolases which liberate arachidonate for eicosanoid biosynthesis.