The effects of α-linolenic acid enriched diets on the lipid composition of rainbow trout (Oncorhynchus mykiss) muscle and liver were determined. Diets containing 0, 4, 10 or 20% (wt/wt) linseed oil were fed to 280 trout for up to 64 days. Linolenic acid levels in total lipid, neutral lipid and phospholipid of liver and muscle increased with duration of intake. The linolenic acid content of total lipid in muscle increased from 10 mg to 355 mg/100 g flesh. There was no significant increase in the elongated desaturated products, i.e., eicosapentaenoic or docosahexaenoic acids, in either tissue during the feeding period.