Randomly selected groups of slaughter cattle, crossbreds of dairy (n = 14) and zebu (n = 131) types were classified by age (2.5, 3.0, 3.5 and 4.0 yr., estimated by dentition), and carcass fatness (as described by different criterion, including marbling levels) to study variation in moisture (M), lipid (L), and fatty acid (FA) contents (g/100 g of fresh tissue) of longissimus muscle trimmed to zero fat cover. Overall means +/- standard deviations per 100 g of raw product for M and L were 73.9 +/- 1.36 and 2.9 +/- 1.04, respectively. Analyses of variance by the least squares (LS) method showed age, breed type, marbling, backfat thickness and carcass finish affected (p < 0.05) fatty acid (FA) profiles. The oldest cattle group (4 yr. or older) trended to present a lower intramuscular lipid content (2.72 g/100 g) and showed the highest (2.04) unsaturation (unsaturated/saturated FA) index (p < 0.05). Breed type had little effect on the FA profile. Comparison of LS means showed intramuscular concentrations of myristic and linolenic acids were slightly higher in samples from dairy types (p < 0.05). Carcasses with poor, "patch-like" fat distribution, showed muscles with the highest (0.16) polyunsaturated/saturated FA index (p < 0.05). Unsaturation indexes for trimmed beef samples with the prevailing marbling levels (1.76 for "Traces" to 1.92 for "Devoid") show a clear predominance of unsaturates, relatively larger than that estimated from compositional FA data reported for the same cut in the United States.