Abstract: Observations were made on behavioral patterns of eating, drinking andsleeping of albino rats isolated or housed in groups for 8-9 weeks. Resultsindicated that the patterns of sleeping differed significantly between isolatedand gregarious animals, although the food or water intake and body weightwere similar in both groups of animals. Isolated rats has significantly lesssleep time. The extent of changes in sleep time for isolated rats was largerthan that for gregarious rats. Later both the isolated rats and gregarious ratswere brought together in groups of 4 strangers per cage as a means of socialstress, and its effects on behavioral patterns in both groups were investigated.Behavioral changes of eating, drinking and sleeping induced by social stressfor isolated rats were more significant and restoration was slower than thatfor gregarious rats. Moreover, the isolated rats, when placed together,developed fighting behavior, which gradually disappeared in a number of days.A month later, social stress was again imposed on both groups of animals,the isolated rats developed fighting behavior and sleep time was affected again.

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