In an earlier report of our placebo-controlled selegiline trial on de novo parkinsonian patients, we have shown that the need to start additional levodopa therapy is significantly postponed by using selegiline monotherapy. Now we report the two-year interim results of the double-blind continuation of the trial in 44 patients after the introduction of levodopa to the earlier therapy with placebo or selegiline (21 and 23 patients, respectively). The clinical disability was assessed by three rating scales. The daily dose of levodopa needed to maintain an optimal condition had to be increased progressively up to a 52% higher level in the placebo group than in the selegiline group (543 +/- 150 and 358 +/- 117 mg, respectively, p < 0.001). The number of daily doses of levodopa was also statistically significantly higher in the placebo group during the 24 months' observation period (p < 0.01). The ratio of levodopa doses that was expected to stay the same contrarily significantly increased suggesting that selegiline would, besides having the levodopa potentiating effect, also have a beneficial influence on the progression of the basic cerebral dopamine deficiency. The combination of selegiline and levodopa was well tolerated, and the adverse event profiles did not differ from each other. In conclusion, early selegiline therapy allows a significant saving in the subsequent levodopa dosage. This saving seems to become even stronger along with the treatment time.