The degree to which vocal accommodation occurred in the interaction of mothers with 27 infants 3- to 5-months old equally divided among three diagnostic groups (heart disease, Down Syndrome, and no known abnormalities) was investigated. Videotapes were made of the infants during 3 minutes of face-to-face play with their mothers. Tapes were coded in terms of sequence of vocalizations, pauses, switching pauses, and turns. Time-series regression analyses indicated that a great deal of accommodation occurred, especially for the vocalization and pause parameters. The accommodation was primarily compensatory in nature and was exhibited equally by mothers and infants in all three diagnostic groups. There were also substantial individual differences in vocal behavior across dyads within each group. Findings appeared to support the notion of the importance of interpersonal vocal accommodation in normal individuals and to extend it to some at-risk grous. A 9.5 page reference list is included. (Author/CL)