Evaluation of the medial hamstring reflex (MHR) was included in the routine neurological examination of 52 hospitalized patients with a suspected lumbar disc protrusion. The MHR was tested in the supine patient with the hip slightly flexed, externally rotated and abducted. The ipsilateral knee was semiflexed and supported by one of the examiner's hands. The reflex muscle contraction was elicited by striking the index finger of the supporting hand placed on the tendons in question with a reflex hammer. The positive predictive value of an abnormal MHR as a sign of herniation from the fourth lumbar disc was found to be 85-89 per cent and the negative predictive value to be 51-61 per cent. The corresponding values when considering an abnormal Achilles tendon reflex as a sign of herniation from the fifth lumbar disc were calculated to be 67-84 per cent and 79-84 per cent, respectively. It is therefore recommended to include the MHR in the neurological examination of patients with a suspected lumbar disc protrusion.