This longitudinal, ethological study explores the development of communication behaviors, different types of social peer interactions, and mother-child interaction among 15 boys and 15 girls from 16 through 30 months of age. Each subject was filmed twice each month over a period of 14 months while he or she had lunch with 5 peers. Several subjects were videotaped at home with their mothers in feeding situations when they were between 18 and 24 months of age. Findings indicate that (1) the non-agonistic interactions and the contact-initiating behavior with peers increases significantly at the end of the second year and especially during the first half of the child's third year; (2) from 18 months, agonistic interactions tend to decrease; (3) duration of dyadic interaction is the same as that for polyadic interactions; (4) boys more often than girls are involved in social interactions and contact-initiating behavior with peers; (5) mothers and toddlers make relatively equal contributions to non-agonistic interactions and soliciting behavior; and (6) during the period between 19 through 24 months, the frequency of mother-toddler non-agonistic and agonistic interaction is significantly higher than the frequency of these types of interaction among toddler and peers. However, the percentage of agonistic interaction is relatively the same in mother-toddler and toddler-peer interaction. (RH)