In 50 patients with lumbar nucleus pulposus prolapse the force of femoral abductors was determined by the test of Lovett and by means of dynamometric measurements. In 90% of patients paresis of these muscles was found. A comparison of the incidence of other signs of nerve root damage such as paresis of plantar and dorsal flexion of the foot and toes, sensory impairment on the foot and lack or weakness of ankle jerk showed that paresis of fermoral abductors was most frequent among them. This fact is explained by a particular predisposition for development of uncleus pulposus prolapse at the level of 4th and 5th intervertebral discs with resulting injury to the nerve roots L4, L5, and S1 innervating femoral abductors. The authors think that paresis of femoral abductors may be a pathognomonic sign in the diagnosis of nerve root lesions caused by nucleus prolapse at the levels L4-L5 or L5-S1. The frequency of paresis and the degree of weakness indicate the necessity of motor rehabilitation of this music group in comprehensive treatment of patients with lumbar disc prolapse.