Two feeding trials, with the same diets, were conducted for periods of 4 weeks each to investigate possible interrelationships in control mechanisms of blood cholesterol level by casein and fish oil in young chicks. Comparisons were made between influences of dietary casein vs. soy protein, fish oil(EPA 24.8%, DHA 10.1%) vs. com oil and cholesterol added at levels of 0 vs. 0.3% on plasma and liver cholesterol. The chicks in Exp. 1 were fed the diets ad libitum while those in Eop. 2 were paired-fed to equalize the amount of dietary intake in order to remove any effects arising from differences in feed intake. Chicks consuming the casein in Exp. 1 showed reduced feed intake and body weight gain compared to those fed soy protein diet(P$lt;0.01). The same response in body weight gain was obtained in chicks of Exp. 2. In Exp. 1, casein intake increased total cholesterol in the plasma and liver(P$lt;0.05), mainly due to high levels of plasma low density lipoprotein cholesterol(LDL-C). Although fish oil ingestion did not affect plasma cholesterol levels elevated by casein feeding (Exp. 1), paired-feeding of the casein + fish oil diet(Exp. 2) resulted in the same level of total plasma cholesterol as that obtained by the soy protein +- fish oil by lowering the LDL-C. The reduction of casein-induced high plasma cholesterol levels by addition of hsh oil is not enough to confirm the existence of an interrelationship between the control mechanisms of casein and fish oil. Further research needs to be conducted to confirm the observations in the present study.