The objective was to determine the natural variability in beef fatty acid composition and to identify single nucleotide polymorphisms (SNPs) in the stearoyl-CoA desaturase (SCD) gene to test the association of SNPs with fatty acid composition. We have used common gas chromatographic techniques to determine the fatty acid composition of phospholipids and triacylglycerols (TAGs) extracted from beef muscle (longissimus dorsi) from 800 sire-identified cattle originating from Iowa State University beef cattle breeding selection projects. Heritability of individual fatty acids and indexes of fatty acid desaturase and elongase systems were calculated by evaluating specific ratios of fatty acids (product/precursor). In general, we found that TAG composition is heritable, but phospholipid composition is not. The atherogenic index of TAGs as proposed by Ulbright and Southgate had a heritability estimate of 0.55 and 0.45 for the TAG and total lipids, respectively. Individual fatty acids of TAGs also had high heritability estimates. For example, the heritability estimates of 14:0 and 16:0 in TAG were 0.49 and 0.40, respectively. Monounsaturates 16:1 and 18:1 in TAGs both had heritability estimates greater than 0.5. Future research will focus on DNA sequencing of candidate genes from sires that are phenotypically divergent for a trait of interest. Ultimately, we plan to develop DNA markers for use in selecting breeding stock to improve healthfulness of fatty acids in beef. Three SNP candidates in the SCD gene were tested by using Iowa State University beef cattle. Two of the potential SNPs were homozygous in this population (n=123). We have classified 172 cattle into two genotypes, VA and VV, based on the third SNP. The ratio of palmitoleic acid (C16:1) concentration vs palmitic acid (C16:0) concentration of TAG is significantly associated with the SNP (P=0.02). There is no significant association of the SNP with the fatty acid composition of phospholipids.