Predictability and controllability of events influence attributions and affect in many research domains. In face-to-face social interaction, behavior is predictable from actor's own past behavior (internal determinants) and from partner's past behavior (social determinants). This study assessed how affect ratings are related to predictability of vocal activity from internal and social determinants. Time and frequency domain analysis of on-off vocal activity from 55 dyadic gettingacquainted conversations provided indexes of predictability from internal and social determinants. Greater predictability of vocal activity patterns from both internal and social determinants was associated with more positive affect. Future research should take internal as well as social determinants of behavior into account. The study of behavioral dialogues is emerging as an important research paradigm in social, developmental, and clinical psychology (Warner, 1991a). Investigators have examined time series data on the behavior, affect, or physiological states of social interaction partners to assess how social behavior is structured in time and how the behaviors of partners are interdependent.