Juvenile coho salmon were injected intraperitoneally with [1-14C] linolenic acid and sampled at 24, 120, and 240 hr. Liver, heart and gill lipids were extracted analyzed, and halflives of individual liver glycerophospholipids and n-3 fatty acids determined from rates of loss of radioactivity. Incorporation of label into gill was much less than into either heart or liver. Total acyl halflife was shorter for the choline phospholipids than for the ethanolamine phospholipids, as were the halflives of all individual n-3 fatty acids. Eicosapentaenoic acid (20:5n-3) had the shortest halflife in both phospholipids (50-60 hr), while docosapentaenoic acid (22:5n-3) and docosahexaenoic acid (22:6n-3) had much longer halflives. Specific activities of the shorter chain n-3 fatty acids were much greater than the longer, more unsaturated homologs at all times, suggesting possible differences in their mechanisms of incorporation into phospholipids. Diacylglycerol analysis indicated that de novo synthesis could be responsible for the incorporation of only a small portion of the labeled long chain fatty acids found in phospholipids. The fatty acid halflives reported here for salmon are in general agreement with those found previously in mammals.