Abstract How do talkers maintain intelligibility when speaking in the presence of a background conversation? The current study identified acoustic and temporal modifications of speech manifested by interlocutors in the face of competing speech, with and without visual contact. Pairs of talkers held free conversations either alone or in the presence of a second pair. Regardless of the availability of visual information, speaking simultaneously with another talker resulted in overall increases in energy, F0, F1 and a decrease in speech rate. Overlapping with the background pair resulted in an increase in energy but no change in the two prosodic parameters F0 and speech rate. By contrast, within-pair overlap led to an increase in F0 and a decrease in rate, and no change in speech level. The absence of visual cues produced a significant reduction in within- pair overlap, which tended to be greater when the background pair was present. These findings emphasize the need to distinguish between Lombard and interactional influences on acoustic parameters, and suggest that adverse conditions such as competing speech or absence of visual cues cause interlocutors to adopt more careful dialogue strategies, perhaps with the aim of reducing energetic and informational masking at the ears of the listener.