||Physical activity and balance performance were examined in gray mouse lemurs (Microcebus murinus) aging from 1 to 10 years of age. Home cage spontaneous activity, physical and behavioral activities in an open-field test and balance performance at the Rotarod test were evaluated. In this prosimian primate, which life span reaches 8-10 years in captivity, balance performance at the Rotarod test showed a clear decease with age. Latency to fall decreased from 154.7 +/- 13.5 s in the youngest group of animals to 31.2 +/- 5.4 s in animals aging 6 years or more. A significant decrease was noticeable as early as 4 years of age. In a familiar cage, locomotor activity and jumping frequency were reduced in aged animals compared to adults. In contrast, when introduced in an open field, aged animals exhibited an increase in locomotor activity and sniffing frequency when compared to younger animals, while latency to first movement was higher in the adult than in the aged subjects. Based on these results, repeated behavioral testing should be initiated early in the life of this species, in association with an evaluation of visual and olfactory capacities. These findings are important to take into account if detailed evaluations of sensory-motor performances are required in studies on aging processes in primates. (C) 2002 Elsevier Science Inc. All rights reserved.