There is no commonly accepted reflex from L5 innervated muscles. Hamstring muscles are primarily innervated by the L5 and S1 roots. It is shown that in the presence of symmetrically active gastrocsoleus reflexes, asymmetry of the hamstring reflexes indicates an L5 root lesion. We describe a method for eliciting the medial hamstring reflex by percussing the conjoint tendon of the semitendinosus and biceps femoris muscles at the level of the ischial tuberosity. Electromyographic, myelographic, and operative data confirmed the presence of an L5 root lesion in 7 patients with asymmetric hamstring reflexes.