It has earlier been claimed that clinical improvement of patients with Parkinson's disease is obtained by treatment with NADH. This has to be verified by double-blind, clinical studies and measurement of biochemical effects of the treatment. In a double blind study five patients with clinically moderate Parkinson's disease were treated with NADH, 25 mg, given intravenously once a day for four days. Then they were given 25 mg NADH intramuscularly after 2 and 4 weeks. Disability scores were determined before each treatment and two weeks after the final injection. A control group (n = 4) with the same degree of Parkinson's disease obtained sodium chloride with the same schedule. According to the Unified Parkinson's Disease Rating Scale a tendency to clinical improvement was seen after the iv infusions in both treatment and placebo groups. However, the changes were not statistically significant, and no changes occurred during the following weeks. No changes were found neither in the study nor the control group regarding cerebrospinal fluid concentrations of dynorfin, metenkefalin, somatostatin, hydroxy-methoxy-phenylglycol, homovanillic acid and 5-hydroxyindole acetic acid. The results indicate that no great changes are obtained after short-term treatment of parkinsonian patients with NADH, neither clinically nor biochemically.