Social preference was assessed across 9 weeks in domestic chicks which were either living with a live companion (another chick or a guinea pig) or in isolation. Experimental chicks lived for 3-week periods with the original companion, with an alternate companion of a different species, and again with the original companion. Control subjects lived continuously with their original companion or in isolation. Weekly preference tests initially indicated strong preference for the original companion, regardless of the biological appropriateness of the species of the companion, although controls living in isolation tended to prefer the chick. Preference waned but did not reverse for experimental chicks living with the alternate companion during the 2nd period, whereas original preference continued for controls. Returning the subjects to the original companion in the 3rd period did not reestablish the original preference.