An emergent qualitative design provided the scaffolding for the micro-analysis of video footage and subsequent video-cued discussion with four reviewers. The collated material was used to prepare thick descriptions which were annotated for infant and therapist behaviours. A further thematic analysis of these behaviours provided 14 sets of behaviours used by the medically fragile newborn infants to indicate availability for interplay and 20 sets of behaviours used by the therapist in response to the infant. The interaction of these categorised behaviours provided seven markers of interplay between the music therapist and the medically fragile newborn infant.