Changes in dietary fatty acid composition alter phospholipid fatty acid composition in a variety of tissues, but little attention has been paid to skeletal muscle. In this study, rats were fed for 9 wk one of three isoenergetic diets: an essential fatty acid-deficient diet, a diet high in (n-6) fatty acids, and a diet enriched with (n-3) fatty acids. Some rats from each group were fed a nonpurified diet for a further 2 or 6 wk. Neither body mass nor food consumption varied among the dietary groups at any stage. Analyses of total phospholipids in soleus (a "slow" twitch muscle) and extensor digitorum longus (a "fast" twitch muscle) revealed that after 9 wk of test diet consumption, muscle phospholipids from rats fed the essential fatty acid-deficient diet were deficient in essential polyunsaturated fatty acids (triene:tetraene ratio >0.5), whereas the polyunsaturated fatty acids in muscle phospholipids from rats fed the high (n-6) fatty acid and high (n-3) fatty acid diets reflected the composition of their respective diets. Nevertheless, phospholipid fatty acid compositions of seemed to be selectively dynamic. After recovery, although the phospholipid fatty acid compositions of all groups were similar, they all contained a much higher proportion of (n-3) fatty acid than provided in the diets. Overall, these results demonstrate that in rats, the fatty acid profile of skeletal muscle phospholipids is strongly influenced by dietary changes, with most effects being reversible after short periods of adequate dietary intake.