The aim of this investigation was to ascertain possible inhibitory effects of the antimycotic agent croconazole on eicosanoid biosynthesis. Human polymorphonuclear leukocytes (PMN) and whole blood of healthy donors were pretreated with croconazole in different concentrations (0.8-100 μM) for 5 min followed by the addition of Ca ionophore A23187 (10 μM) and subsequent incubation for 10 min (PMN) and 30 min (whole blood), respectively. Thereupon the eicosanoids were determined by reversed-phase high-performance liquid chromatography. Croconazole exhibited dose-dependent inhibitory activity on the 5-lipoxygenase (5-LOX) of neutrophils. The mean half maximum inhibition concentration (IC50) of croconazole for synthesis of leukotriene B4 (LTB4) and 5-hy-droxyeicosatetraenoic acid (5-HETE) was determined as 7.8 ± 1.7 and 7.6 ± 0.3 μM, respectively. The mean IC50 value for LTB4 estimated in whole blood was distinctly higher (27.0 ± 3.1 μM) compared with that determined in PMN. Additionally, an inhibitory effect (IC50 9.8 ± 2.0 μM) on the production of the cyclooxygenase (COX) product 12-hydroxyhepta-decatrienoic acid (HHT) was demonstrated, whereas the production and/ or releasing of 12-hydroxyeicosatetraenoic acid (12-HETE) was not attenuated by the azole. Our results in the cell-free 5-LOX system favor a direct inhibitory action of croconazole on 5-LOX, with a relatively high portion (45-77%) of reversibility. In spite of distinctly lower inhibitory potency compared with reference inhibitors such as nordihydroguaiaretic acid and indomethacin, croconazole is an effective inhibitor of arachidonic acid metabolism. Our results suggest that croconazole may be of some benefit in anti-inflammatory therapy.