The accurate diagnosis of lumbar radiculopathy in intervertebral disc herniation remains a significant problem In an attempt to aid the diagnosis of the proper roots which responsible for the clinical symptoms, somatosensory evoked potential has been used in conjunction with standard diagnostic technique in 21 patients with herniated nucleus pulposus. And the results were compared with the surgical findings of the patients and with the results of control group of 25 normal adults.

1) Latencies of P1 in normal adults were 38.6 msec in L4, 38 msec in L5, and 39.7 msec in S1 nerve root in average.

2) Latencies of P1 in the 23 compressed roots were 39.2 msce in L4 42.3 msec in L5, and 41.4 msec in S1 roots in average. But the delay of latency was significant in L5 only (P<0.01). 3) Latency of P1 in 23 compressed roots were delayed significantly to 41.9 msec than 39.8 msec in unaffected side of same patients(P<0.05)

4) The diagnostic accuracy for the compressed nerve roots, compared with surgical findings was 78%

From the above results, the author concludes that the P1 latency of the affected side should be compared with that of the unaffected side of same patient than that of normal persons, for the diagnosis of compressed nerve roots in herniated nucleus pulposus.