Twelve parkinsonian patients (6 men and 6 women), mean age 60.5 years, range 47-72, were examined with autonomic test when de novo and after 2 years of continuous levodopa treatment. They were all free from any disease interfering with autonomic examination. When de novo they had a significant decrease of heart rate response to deep breathing and to laying to standing tests if compared with an age- and sex-matched control group (15.6 +/- 8.8 vs. 28.6 +/- 12.1, P less than 0.01 and 7.0 +/- 7 vs. 14.2 +/- 5, P less than 0.01). After 2 years of levodopa treatment they had a non-significant decrease of heart rate response to deep breathing test (21.8 +/- 10.6, P N.S.) and a still significant decrease of heart rate response to laying to standing test, but at a lesser level (7.7 +/- 7.0, P less than 0.05). Furthermore, they showed a significant decrease of the systolic and MAP orthostatic pressure to tilting table (-9.2 +/- 12.0 vs. +4.9 +/- 8.9 and -4.5 +/- 8.4 vs. +4.7 +/- 5.1, both P less than 0.01) probably due to medication. The other tests were never significant. We hazard as possible explanation an action of levodopa on dopaminergic neurons in the nucleus dorsalis of vagus.