The solution of problems which include both exible and rigid bodies is addressed in this paper. An explicit time integration scheme along with a ÿnite element semidiscretization procedure is employed for the exible bodies, whereas an implicit conserving scheme is adopted for the rigid bodies. For elements in each exible body which lie on an interface with a rigid body, a node-based partitioning scheme is introduced. In each half-time step where the balance of momentum is enforced, the explicit nodes are integrated ÿrst. The results are used subsequently as boundary conditions for the integration of the implicit nodes. The implicit nodes which lie on an interface of a rigid body are constrained to follow the motion of the rigid body by a Lagrange multiplier method. This leads to a modiÿcation of the inertial properties of the attached rigid body, and results in an iterative solution procedure involving six parameters: three for translations and three for rotations. The overall algorithm is shown to be momentum conserving. Model problems are presented for examining the applicability and the conserving property of the scheme.