This study analyzed overlap (or interruption behavior) in conversations between mothers and their stuttering children to determine how overlap relates to fluency. Subjects for the study, which is part of the Genesis of Stuttering Project, were 20 preschool stuttering children and their mothers. Three forms of overlap were examined: simultaneous start, the parent or child as interruptee, and the parent or child as interruptor. Both subjects and control group children demonstrated more disfluency during overlapped utterances than nonoverlapped utterances. Most disfluency and stuttering occurred during overlap rather than immediately preceding or following it. There were no differences by sex. Mothers of stutterers interrupted their children's dysfluent speech significantly less than did the mothers of nonstuttering children, and there were no differences between the mothers during fluent speech. It is concluded that the data do not support the contention that stuttering/dysfluency evokes overlap or interruption, but overlap does appear to evoke stuttering/disfluency for both stuttering and nonstuttering children. (Five references) (JDD)