A 6-week experiment on rats was performed to evaluate the growth-promoting and cholesterolaemic activity of olive and linseed oils mixed with pure myristic, palmitic or stearic acids. Each oil was mixed with each acid in a 1:1 w/w ratio. At the end of the experiment, blood was collected by cardiac puncture and total serum cholesterol (TC), HDL and LDL fractions, and serum triacylglycerols (TAG) were estimated. Mixing oils with pure fatty acids resulted in higher body weight gains. The longer the carbon chain of the acid, the higher were the body weight gains of the rats (1.99, 2.39 and 2.57 g per day for C₁₄, C₁₆ and C₁₈, respectively). Myristic acid gave the highest level of TC (84.5 mg dl^-1), while its mean content in pure fatty acids was only 77.34 mg dl^-1. Myristic acid also accounted for the largest increase of TAG content in the case of both oils.