Interactions with companion animals have been shown to have socializing and calming effects for Alzheimer's patients in an institutional setting. Sixty-four Alzheimer's patients living in the private home were studied, through medical records and information provided by caregivers, to determine what effect association with a companion animal had on the progression of cognitive decline and the manifestation of concomitant noncognitive symptoms. Prevalence of episodes of verbal aggression and anxiety was reported less frequently in 34 patients who were exposed to companion animals compared with patients who were not exposed. Significantly fewer mood disorders were reported in patients who were attached to their pets compared with patients who were not attached. There was no significant difference in the rate of cognitive decline between pet-exposed and nonexposed patients as measured by three standard indices. This study lends preliminary support to the belief that interaction with pets can aid in tempering feelings of agitation and aggression in Alzheimer's patients.