Many disorders of the shoulder complex are accompanied by changes in the pattern of scapular motion which is difficult to measure except radiographically. In order to study the three-dimensional motion of the scapula which accompanies arm movements, a technique has been developed using a three-pointed locater which can be applied over three bony landmarks - the acromial angle, the inferior angle, and the root of the scapular spine. The spatial orientation of the locater relative to the trunk was measured using an electromagnetic movement sensor (isotrak) which has been shown to be clinically reliable. Measurements of scapular plane rotations during abduction showed particularly good agreement with published data; variations in measurements of the out-of-plane angles were attributed to difficulties of contacting the acromion reliably when the deltoid muscle was contracted. It is concluded that the system is suitable for clinical use in the study of shoulder pathology.