Concomitancy is one of several factors to measure when performing a complete diagnostic evaluation of heterotropias and heterophorias. When the fusion-free position of the eyes varies significantly in magnitude or direction in different fields of gaze, nonconcomitancy exists. Frequently the testing of concomitancy is overlooked or performed with little precision. Yet, concomitancy testing is important because the existence and amount of nonconcomitancy may influence the prognosis, therapeutic approach, and success in treatment, and may indicate some life-threatening systemic problem which requires referral. A specially designed light-emitting diode target screen was combined with the projection system of the B & L Autoplot. This system allows the Hess-Lancaster test to be performed quickly and accurately with automatic recording of the patient's responses.