The maternal behavior of 4 monkeys separated from their mothers at birth and denied opportunity to interact with other monkeys during the first 18 mo. of life is described and compared with the maternal behavior of 4 normal feral monkeys. The 4 socially deprived monkeys were grossly inadequate mothers, but the social development of the infants of these inadequate mothers was apparently normal. The maternal behavior of 5 additional mother-deprived monkeys is also described; 3 of these animals were inadequate and 2 adequate mothers. The 2 adequate mother-deprived mothers had early social experience; the 7 inadequate mothers did not. 3 inadequate mothers gave birth to a 2nd infant and exhibited normal maternal care. (PsycINFO Database Record (c) 2006 APA, all rights reserved)