The incorporation of tritiated palmitate into disaturated phosphatidylcholines was studied in alveolar macrophages from rats. Disaturated phosphatidylcholine synthesis was assessed in the absence and presence of a variety of foreign substances and chemical mediators including zymosan, acetyl-B-methylcholine, and N6-O2- dibutyryladenosine-3',5'-cyclic-monophosphate. Incorporation of the labeled palmitate into the disaturated compound in isolated alveolar macrophages increased rapidly for approximately 30 minutes and reached a maximum after approximately 2 to 3 hours of incubation. The external level at which one half maximal incorporation occurred (K1/2) for palmitate, determined from a double reciprocal plot, was millimolar in alveolar type-II cells. The incorporation of palmitate, choline, and glycerol into disaturated phosphatidylcholines in alveolar macrophages was comparable to that in alveolar type-II cells. Zymosan stimulated palmitate incorporation by approximately 90 percent. Cholinergic and beta- adrenergic agonists had no effect on the incorporation of palmitate into the disaturated phosphatidylcholines. Catabolism resulted in the formation of palmitate and water soluble choline derivatives and was enhanced in the presence of unlabeled choline, palmitate, or oleate. The authors conclude that alveolar macrophages synthesize disaturated phosphatidylcholine and release the compound into the extracellular space.