Social interaction analysis was used to evaluate the social effect and function of the Staccato Grunt vocalizations (Chevalier-Skolnikoff 1974) of stumptailed macaques (Macaca arctoides). Staccato Grunts are used in the highly specific context of an individual expressing friendly interest in an infant stumptailed macaque, as demonstrated in a previous quantitative descriptive study (Bauers 1989). It was hypothesized that these vocalizations function to signal an actor's benign intent when expressing Interest in Infants, that the signals are directed to the infant's mother, and that their use lowers the probability of an aggressive response from the mother. The functional hypothesis predicts that 1. mothers would not direct Staccato Grunts to their own infants; 2. Staccato Grunts would be given with higher probability when the mother of an infant is near (< 1 m), and 3, a mother's tolerance for attention or physical contact directed to her infant should be facilitated by Staccato Grunts. These predictions were supported by the data, based on analysis of the conditional probabilities of two-event sequences in 554 interactions. It is concluded that Staccato Grunt vocalizations are used pragmatically to acquire access to infants and to reduce the probability of aggressive responses from their mothers. Acoustic characterization of Staccato Grunts, and alternative interpretations of the behavior are discussed.