SUMMARY—The fatty acid composition of porcine longissimus dorsi muscle lipid was determined for 30 animals slaughtered at two live weights (49.6 and 94.1 kg) and consisting of an equal number of boars, barrows, and gilts. The lipid was separated into the neutral lipid and phospholipid fractions prior to analysis.Odd‐numbered fatty acids Cl1, C13, C15, and Cl7 were significantly higher in the phospholipid fraction. Fatty acid Cl7 was never detected in the neutral lipid fraction.Both weight and sex effects were quite restricted to the neutral lipid fraction. Weight had a significant effect on amount of fatty acids C10, C11, C12, C14, C16, and Cl8 in one or more of the sexes. The most interesting result was the marked increase in fatty acid Cl8 of the heavy (94.1 kg) gilts and barrows over its very constant level in the muscle from boars of both weights. This difference, coupled with significantly lower C18–1 values in heavy barrows and gilts than in boars, resulted in a markedly higher mean ratio of fatty acid C18–1 to Cl8 for heavy boars. Thus these data suggest that much of the increase in saturation of intramuscular lipid that occurs after about 5.5 kg live weight can be attributed to the ratio of fatty acid C18–1 to C18. This change is probably dependent upon sex hormones and is restricted to the neutral lipid