Lipid hydrolysis with formation of free fatty acids occurs rapidly in frozen cod fillets at +10°F, and slowly at −10°F. In fatty fish the free fatty acid development is slower but still temperature dependent. It appears that when appreciable lipid hydrolysis occurs on storage usually the actomyosin extractability, as well as taste panel scores, decreases. Contrary to most previous results, there was no loss in actomyosin extractability or taste panel acceptability up to a year and a half in the frozen cod at −10°F.