The protein concentration in the cerebrospinal fluid (CSF) is often increased in patients with sciatica, probably due to leaking of plasma proteins through the blood-nerve root barrier into CSF. Positive straight leg raising test, paresis, altered sensibility, reduced reflexes, and type of treatment were related to the CSF protein concentrations in 180 patients with sciatica caused by verified lumbar disk herniation. Significantly higher values of the CSF/serum albumin ratio and the CSF/serum immunoglobulin G ratio were found both in patients with positive straight leg raising test results and paresis compared with patients with no clinical findings. In the patients who had undergone emergency surgery, the same ratio parameters were significantly higher when compared with those who had undergone routine surgery and those had not undergone surgery. Elevated CSF proteins seem to be important indicators of the functional status of the nerve root and a measure of the degree of seriousness of sciatica. The interaction of smoking on CSF proteins was also studied.