The fatty acid composition of serum cholesteryl esters is used as a qualitative biomarker of fatty acid intake, but quantitative data are scarce. Between 1987 and 1992, the authors fed various fatty acids in four controlled trials to 232 healthy Dutch volunteers and measured the proportion of fatty acids in participants' cholesteryl esters. Each 10% of energy fed as linoleic acid (18:2) raised the proportion of linoleic acid in cholesteryl esters by 9.3 g per 100 g of fatty acids (standard deviation (SD) 3.1). For oleic acid (cis-18:1), this figure was 6.5 g/100 g (SD 1.7); for trans fatty acids (trans-18:1), it was 1.1 (SD 0.5); for stearic acid (18:0), 1.0 (SD 0.4); for palmitic acid (16:0), 1.7 (SD 0.5); for myristic acid (14:0), 2.1 (SD 0.7); and for a mixture of saturated fatty acids (12:0, 14:0, and 16:0), it was 2.2 g/100 g (SD 1.0). The coefficient of variation of the responses was fairly constant, indicating that changes in intake for each of these fatty acids can be monitored with similar precision. These data can be used to estimate the degree of compliance in experimental studies involving exchanges of single dietary fatty acids. Most fatty acids in cholesteryl esters may also be used in observational studies to estimate differences in intake. However, because of multiple simultaneous differences in fatty acid intake between free-living individuals and between populations, such data cannot provide information on absolute intake of fatty acids.