The effect of intratracheal administration of fly ash has been studied on lung micro‐somal and lung surfactant phosphatidylcholine (PC) metabolism in rats using [methyl‐14C]choline and [methyl‐14C]methionine. Fly‐ash administration significantly increased total phospholipids, PC, phosphatidylethanolamine (PE), and phosphati‐dylglycerol (PC) of lung surfactant. Fly‐ash administration stimulated the formation of lung microsomal PC (as measured by the incorporation of labeled precursors) both by the cytidine 5'‐diphosphate (CDP)‐choline pathway and by the N‐methylation pathway, but this stimulation was fourfold higher in the latter case and only twofold higher in the former as compared to the control. Likewise, the secretion of PC formed by the N‐methylation pathway was sixfold higher as compared to the control whereas secretion of PC formed by the CDP‐choline pathway was only threefold higher as compared to the control. Fly‐ash administration further increased total saturation and decreased unsaturation in PC, PE, and lysophosphatidylcholine (LPC) of lung and in PC, PE, LPC, and PC of lung surfactant as compared to the controls.