Previous studies have reported that the maternal behavior of rhesus monkey females who themselves were reared without mothers ("motherless mothers") is generally inadequate and often abusive. The present study examined the maternal competency of SO such subjects with respect to the variables of rearing environment, age at first social contact, sex of offspring, age at first delivery, parity, and duration of exposure to previous offspring. The results suggested that physical contact with conspecifics, either with peers prior to adulthood or with their own infants immediately after birth, greatly reduced the probability that motherless mothers would be inadequate maternally.Researchers who have studied the consequences of social deprivation in rhesus monkeys are in virtual agreement that social isolation or restriction imposed early in life has devastating, and often permanent, effects on the social development of monkeys. As adults, monkeys reared for at least the first 6 months in physical isolation from conspecifics have been reported to exhibit anomalies in home-cage behavior (Cross & Harlow, 196S;Suomi, Harlow, & Kimball, 1971), in adaptation to novel environments (Harlow, Schiltz, & Harlow, 1969), in approach to complex stimuli (Sackett, 1972), and in suppression of ongoing response chains (Sackett, 1970). With respect to social activities, adult isolate-reared monkeys typically display excessive and inappropriately directed aggres-