This paper studies force-closure grasps of rigid objects by using two palms. The two palms are instrumented with tactile sensors capable of detecting the presence of contacts, and are assumed to be respectively installed on two robotic manipulators capable of motion and force control. Established in this paper is an existence condition under which the two palms form a force-closure grasp. The salient feature of this condition is that it does not require the information on the shape of the object and the contact locations. A configuration of the two palms in contact with the object satisfying this condition is called a force-closure grasp configuration (FCGC). Further an algorithm is developed to check the condition for FCGC in terms of the position and orientation of the palms.