Platelet activating factor (PAF) and 1-O-alkyl-linked choline-containing phosphoglycerides have been identified in the blood of the lizard, Anolis carolinensis. The level of PAF in the blood of chronically stressed lizards is 250% higher than in that of controls; the blood contains sufficient 1-O-alkyl-linked choline-containing phosphoglycerides to support the synthesis of PAF. Incorporation of PAF is higher in the liver than in the blood; control animals incorporate more PAF than chronically stressed animals. "Lyso"-PAF is the major metabolite in the blood; whereas, in the liver both "lyso"-PAF and "acyl"-PAF are predominant products. 1-Alkyl-2-acetyl-sn-glycero-3-phosphocholine:acetylhydrolase activity in the chronically stressed or corticosterone-implanted lizards is increased 2- to 3-fold over the control. Involvement of PAF in the physiological response to psychological stress is indicated.