In the metabolism of triacylglycerol (TG)-rich lipoproteins, 2-monoacylglycerols (2-MG) are produced by lipoprotein lipase (LPL) hydrolysis of TG. The metabolic fate of 2-MG is not known with certainty. 2-MG that accumulate on the chylomicra surface have been proposed to isomerize spontaneously to 1(3)-MG, which are then hydrolyzed by LPL to free fatty acids and glycerol. In this study the rate and the effect of acyl chain saturation on the spontaneous acyl migration of 2-MG in in vitro model chylomicra emulsions were determined. After 1 h of incubation at 37 degrees C, less than 20% of 2-monoolein (2-MO) or 2-monopalmitin (2-MP) spontaneously isomerized to 1(3)-MO or 1(3)-MP, respectively. Accordingly, it was concluded that spontaneous isomerization of 2-MG is not the major mechanism for 2-MG metabolism post-TG hydrolysis in chylomicra. Isomerization rates, expressed as decrease in percentage of 2-MG remaining per hour, were -5.12 and -5.86 in water, and -0.43 and -0.41 in hexane for 2-MO and 2-MP, respectively. There was no significant difference between the isomerization rates of 2-MO and 2-MP. Thus, in the present study, saturation of the MG acyl chain did not influence spontaneous acyl migration in either water or hexane, but isomerization of 2-MG was faster in water than in hexane.