Serum levels of several n-6 and n-3 polyunsaturated fatty acids were compared in male Wistar muricidal (Mu) and non-Mu rats. The Mu behavior was either spontaneous or induced by long-term isolation, feeding with a starch-enriched polyunsaturated fatty acid diet (PUFA+S), water restriction, or adrenalectomy (ADX). Arachidonic acid (ARA) levels were lower in diet-induced (PUFA+S) Mu rats than in their non-Mu controls. Total n-6 fatty acid levels were also lower in spontaneously Mu rats than in spontaneously non-Mu rats. Docosahexaenoic acid (DHA) and total n-3 fatty acids levels were lower in rats with isolation-induced Mu behavior. The n-3/n-6 ratio was higher in spontaneously Mu rats than in spontaneously non-Mu rats. The changes in ARA levels were greater than those in DHA levels, possibly due to the higher blood-brain barrier passage of arachidonic acid. The results were analyzed in the light of recent results showing a role of PUFAs in human and animal behavior.