Guinea pig lung cells have been obtained by enzymatic digestion of lung tissue and type II pneumocytes have been purified by centrifugal elutriation and adherence on Petri dishes coated with guinea pig IgG. The cells have been characterized by histochemical staining of alkaline phosphatase and by electron microscopy. Arachidonic acid metabolism was studied by incubating purified type II pneumocytes with exogenous arachidonic acid in the presence or absence of calcium ionophore A23187 or with leukotriene A4. The reverse phase high performance liquid chromatography profiles of cells stimulated with calcium ionophore and/or arachidonic acid did not show peaks co-eluting with authentic leukotrienes, which suggested that these cells do not express 5-lipoxygenase activity. On the other hand, type II pneumocytes converted exogenous leukotriene A4 into leukotriene B4; a small amount of peptido-leukotrienes, accounting for less than 5% of total leukotrienes produced, was also detected. It is suggested that transcellular metabolism of leukotriene A4 between type II pneumocytes and other lung cells containing the 5-lipoxygenase may contribute to the previously reported LTB4 production by guinea pig lungs. The type II pneumocyte purification technique described represents a useful alternative to cell culture for studying arachidonic acid metabolism and other cell functions.