Experiments were conducted to compare energy utilization, growth and tissue composition of chicks fed diets containing 10 or 20 parts of either high erucic acid rapeseed oir 24 days. Results showed that chicks fed diets containing 10 or 20 parts LER grew at the same rate, utilized energy just as efficiently, had similar heart to body weight ratios and levels of heart lipids equal to or less than chicks fed comparable diets containing SFO. The substitution of 10 or 20 parts HER for an equienergetic amount of SFO depressed gorwth, feed consumption and carcass fat deposition but had no effect on level of cardiac lipid or relative heart size when fed from 4 to 11 days of age. When fed from 4 to 25 days of age, chicks fed 20 parts HER grew slower, consumed less feed, and when pairfed, deposited less carcass fat, utilized energy less efficiently, had increased heart to body weight ratios but a lower level of cardiac lipid than chicks fed comparable diets containing SFO. Irrespective of the type of rapeseed oil or of the age of the chick, heart lipids contained less erucic acid than carcass fat, indicating that chick heart is as capable of disposing of erucic acid as carcass tissue. It was also found that irrespective of the diet fed, a greater percentage of erucic acid appeared to be oxidized than of eicosenoic acid.