Examined are developmental changes in infants' strategies for using adults instrumentally to achieve goals. Data were derived from longitudinal observations of 1 girl and 1 boy twin individually interacting with 21 somewhat or totally unfamiliar adults at 2- or 3-week intervals from the age of 4 to 15 months, inclusive. Videotapes of interactions were viewed by four observers paired randomly and working independently. Findings indicated an increase in agreement between observers as infants grew older. The manner in which babies attempted to influence adults suggested that babies as young as 4 to 6 months of age may engage multiple means to use adults to implement goals. While babies at the earliest age use adults as tools without obvious acknowledgement of the existence of the other as a person, babies as young as 6 months may use more sophisticated strategies that are less direct and more communicative, such as self-initiated eye contact and symbolic gestures. It is not until the end of the first year that the infants used sustained and complex conventional symbols such as symbolically demonstrating the action to be performed or using words or nods. All the infants, even the youngest, were persistent. (RH)