Our objective was to assess the mechanical changes associated with spasticity in elbow muscles of chronic hemiparetic stroke survivors, and to compare these changes with those recorded in the ankle muscles of a similar cohort. We first characterized elbow dynamic stiffness by applying pseudorandom binary positional perturbations to the joints at different initial angles, over the entire range of motion, with subjects relaxed. We separated this stiffness into intrinsic and reflex components, using a novel parallel cascade system identification technique. In addition, for controls, we studied the non-paretic limbs of stroke survivors and limbs of age-matched healthy subjects as primary and secondary controls We found that both reflex and intrinsic stiffnesses were significantly larger in the stroke than in the non-paretic elbow muscles, and the differences increased as the elbow was extended. Reflex stiffness increased monotonically with the elbow angle in both paretic and non-paretic sides. In contrast, the modulation of intrinsic stiffness with elbow position was different in non-paretic limbs; intrinsic stiffness decreased sharply from full- to mid-flexion in both sides then it increased continuously with the elbow extension in the paretic side. It remained invariant in the non-paretic side. Surprisingly, reflex stiffness was larger in the non-paretic than in the normal control arm, yet intrinsic stiffness was smaller in the non-paretic arm. Finally, we compare the angular dependence of paretic elbow and ankle muscles, and show that the modulation of reflex stiffness with position was strikingly different.