Bolus injections of leukotriene B4 (LTB4) at 30-min intervals repeatedly induced similar profound and reversible neutropenias. In contrast, after a 30-min infusion of LTB4, the neutropenia induced by bolus injections of LTB4 was inhibited in a dose-dependent manner; a threshold inhibition was seen at the infusion rate of 10 ng LTB4/min/kg, whereas almost complete inhibition was observed at 50 ng LTB4/min/kg. Steady state arterial plasma concentrations of LTB4 increased proportionally to LTB4 infusion rate, ranging from 0.15 +/- 0.01 nM (control) to 2.80 +/- 0.16 nM (100 ng/min/kg). Extending the infusion period of LTB4 up to 330 min did not result in an enhanced inhibition of the neutropenia in response to bolus injections of LTB4. Reversibility of the desensitization was shown by an almost complete recovery of the neutropenic response within 30 min after cessation of the infusion. The desensitization achieved towards LTB4 showed some specificity, inasmuch as a profound and reversible neutropenia was observed in response to a bolus of either FMLP or C5a under conditions in which sensitivity to LTB4 was lost. These findings suggest that a specific desensitization to LTB4 is feasible in vivo and may constitute a useful approach, in addition to the use of 5-lipoxygenase inhibitors and LTB4 antagonists, to delineate the significance of LTB4 as a mediator of inflammation.