Eight troops containing a total of 151 howler monkeys were studied for 513 h between December 19, 1970, and February 25, 1971. The troops contained 26 mothers with their infants. Mother-infant and other adult female-infant interactions were analyzed for infants from all three age classes. The data extend the knowledge of howler behavior in three ways. First, the study broadens the comparative data on Alouatta palliate to cover a new geographic area, a coastline forest in southwestern Panama. Second, the data provide the most detailed description of infant behavioral development and mother-infant interactions available in the howler literature. And third, since the population density of 10.4 howlers per ha at the study site is one of the highest densities reported in the primate literature, the present study contributes to the analysis of how primates adapt to conditions of high population density. Comparisons are made between the adult female-infant interactions observed on Barro Colorado Island and those observed at the present study site.