The aim of this study is to examine the sensitivity and characteristics of F-wave abnormalities detected by using various parameters in patients with lumbosacral radiculopathies and to evaluate the relationship with needle EMG or clinical findings. The study was performed on 100 patients with lumbosacral disc herniation. Out of 100 subjects 95 had lumbosacral radiculopathies (single lesion of L5 in 37, S1 in 47, double lesions of L5 and S1 in 11), which were confirmed by operation (some were confirmed by myelogram). Remaining 5 had no definite root lesion. F-waves were recorded by stimulating peroneal and tibial nerves at the ankle. Minimal latency (Fmin), maximal latency (Fmax), latency difference between Fmin and Fmax (Fdif), mean duration (Fdur) and difference between sides in Fmin and Fmax were measured. Conventional motor nerve conduction velocity (MCV) and needle EMG were also examined. A rather high value of 70% in sensitivity was attained by evaluations of Fmin, Fmax, Fdif and Fdur on the affected side. Although the difference between the sides gave us additional information, F-waves from the non-affected side were not always normal. F-wave abnormalities did not correlate with both needle EMG and clinical findings. In conclusion, F-wave study is clinically useful in evaluation of radiculopathy independent of needle EMG or clinical findings.