In a large French hospital, a group of professional experts (including physicians and software engineers) are working on the computerization of a blood-transfusion traceability device. By focusing on a particular moment in this slow process of design, we analyze their collaborative practices during a work session. The analysis takes a praxeological and interactionist approach and is inspired by discussions on the role of artifacts in social practices currently developed within various research frameworks in this field: activity theory, distributed cognition, conversation analysis, and actor network theory. After a brief presentation of the place of objects and artifacts in these ways of approaching action and human cognition, we show how the collective activity analyzed here is generated by the interweaving of discursive, gestural, and artifactual resources.