This study examines the communicative role of crying by assessing the ability of infants to indicate different degrees of distress in different social circumstances. Behaviors of mother-infant pairs were observed in the home for 7-h periods when the infants were 2, 3, 4, and 5 wk old; and three weekly observations were made when the infants were 1 yr old. A Cry Responsiveness Index (CRI) was derived to quantify the degree to which a baby cried differentially during each observation. This statistic showed significant individual differences. The CRI scores were correlated with maternal measures during the early weeks and negatively correlated with ''mother ignore'' at one year. The CRI scores were unrelated to the total amount of crying. The results indicate that responsive infants have responsive mothers-or conversely, that responsive mothers have responsive infants. Thus, cry responsiveness is not a function of infant behavior alone but is inherently an expression of the dynamics of the mother-infant interactional system.