In this study, the actuator related singular configurations (ASCs) of a system of two cooperating SCARA manipulators, are investigated. The ASC concept was First developed for planar pairs of cooperating manipulators, and it was shown that these ill-conditions could be different from the kinematic: singularities. (Ozkan B, Ozgoren MK. Torque related singular configurations of a planar system of two coodinated manipulators. In: Proceedings of International Machine Design and Production Conference, Sept. 9-11, Ankara. Turkiye. 1998). Afterwards, this concept was applied To the spatial systems. (Ozkan B. Ozgoren MK. Actuator related singular configurations of a system of two cooperating SCARA manipulators. In: Sixth International Conference on Mechatronics and Machine Vision in Practice, Sept. 1-3, Ankara, Turkiye, 1999). In this study, the ASCs of the systems of two cooperating SCARA manipulators are examined as an application of the ASC phenomenon for the spatial systems. Also, the ''invalid" actuation arrangements of this system are also investigated. However, systems: with different manipulators can also be treated similarly. (C) 2000 Elsevier Science Ltd. All rights reserved.