This study examined the effects of group composition based on the learners' personality types as measured by the Myers-Briggs type indicator as they interacted in threaded discussions. Three groups comprised introverts, extroverts, and mixed introvert-extrovert classifications. Ninety-six participants were divided into 24 groups of 4 participants each: 8 introverted, 8 extroverted, and 8 mixed. Dependent measures included number of posted messages, social, interactive, cognitive, and metacognitive interaction as measured by Henri's (1992) scheme for coding the type of interaction. Participants in the mixed and extroverted groups posted more messages than those in the introverted group. The extroverted and mixed groups' learners showed more social, interactive, and cognitive interaction than those of the introverted group. However, the mixed group showed more metacognitive interaction than that of the extroverted group. (Contains 2 tables.)