We evaluated the metabolism of exogenous arachidonic acid in polymorphonuclear leukocytes from psoriatic patients in comparison with those from normal subjects. The leukocytes were incubated with 10 microM labelled arachidonic acid and 5 microM A23187 for varying periods of time. We evaluated all the compounds derived from the 5-lipoxygenase activity, including the products of non-enzymatic transformation of leukotriene A4 and w-oxidized leukotriene B4. In the experimental conditions used, there was no significant difference in the formation of any compound at any time of incubation. These results indicate that there is no intrinsic alteration either in 5-lipoxygenase activity or in w-oxidation ability of circulating polymorphonuclear leukocytes in psoriatic patients.