Using audiovisual tapes of 150 actual dental treatment sessions, five dental teams working with handpieces positioned in the 8-o'clock location were compared with five dental teams working with hand pieces positioned in the 12-o'clock location. Criteria used for analysis were frequency and duration of instrument transfer, critical incidents that interfered with instrument movements, and subjective responses of the dental team members. The data showed that the handpiece transfers were faster and more frequent in the 12-o'clock location where they were done via the assistant. However, the reverse was true for transfers of the three-way syringe. Most critical incidents occurred with equal frequency and were common to both rooms, but some were related to instrument location. The subjective responses indicated that the assistant working with the 12-o'clock instrument location had many more tasks and must be more highly trained.