Alterations in dietary fatty acid composition can influence the regulation of metabolism in adipose tissue. To study the effect of dietary fatty acid composition on lipolysis we fed rats diets containing menhaden oil (MO) or coconut oil (CO) for 4 weeks. After 4 weeks on the diets body weight was similar in both groups although epididymal, retroperitoneal and mesenteric fat pad masses were significantly elevated (~30%) in rats fed the CO diet. Epinephrine-stimulated lipolysis was elevated at concentrations >1M in epididymal adipocytes isolated from the MO group. The addition of insulin (10nM) to 1M epinephrine decreased lipolysis to a similar level in both groups. Plasma membrane fatty acid composition was altered to reflect the respective diets. Membranes from the CO fed group were enriched in saturated fatty acids (C10-16) and 18:1n9 and devoid of long chain n3 fatty acids compared to the MO fed group. To examine the effect of altered plasma membrane fatty acid composition on membrane physical properties we used Fourier transform infrared spectroscopy (FTIR). Membrane order was determined in adipocyte plasma membranes from -20 o C to +58 o C. Peak CH 2 symmetric and asymmetric stretching frequencies indicated that below 31 o C membrane order is increased in CO fed animals. When temperature was increased above 31 o C, there were no differences in membrane order between groups. The results of this study suggest that membrane order is not responsible for the lower rate of lipolysis in animals fed coconut oil when both variables are measured at 37 o C.