Anesthesia was used to reduce filial cues to maternal behavior in Macaca fascicularis, and changes thereby in the mothers' behaviors toward their own and alien infants were observed. Effects of infants' general anesthesia on the mothers were obvious in increses in their grooming and sniffing toward younger infants aged 60 days or less, and in decreases in their contact and embrace toward older infants aged 61 days or more. Anesthetized younger infants of the mothers' own were directed contact and grooming more frequently by the mothers than were alien anesthetized younger infants. Aggression was not observed toward the anesthetized infants. Thus, loss of movement in the infants revealed an active role of the mothers of the younger infants to maintain relationships with their offspring, but this active role decreased in the mothers of the older infants. In the second part of the study, an odor of generally anesthetized infants was reduced by hypoesthesia of mothers' olfaction. As a result of this, sniffing decreased toward the younger alien infants and so did grooming toward the younger own infants. The effect of olfactory hypoesthesia in the mothers was thus seen only toward the younger infants, which indicates an active role of young infants' odor in arousing the mothers' positive attention to them.