Homogenates of the placental tissue of near term sheep were separated by 
differential centrifugation into mitochondrial, microsomal and cytosolic 
fractions. The relative proportions of the major neutral lipids and 
phospholipids, together with their fatty acid compositions, were determined in 
the homogenates and in each subcellular fraction. The cytosolic fraction 
contained the highest proportion of cholesteryl esters (CEs) and these possessed 
a fatty acid composition markedly different from the total CEs extracted from 
the homogenate. Both the mitochondrial and microsomal fractions contained 
significant proportions of solvent front phospholipid (SFP) and whereas the 
mitochondrial SFP displayed the relatively unsaturated fatty acid composition 
characteristic of diphosphatidylglycerol (cardiolipin), the fatty acids of the 
microsomal SFP were distinctly more saturated. These results are compared with 
those obtained from other mammalian tissues, both ruminant and non-ruminant, and 
discussed in terms of the function of the components of the subcellular 
fractions.