Twenty patients with paralysis agitans took part in a double-blind, cross-over investigation of CB 154 (2-bromo-alpha-ergocryptine) and Madopar (L-Dopa + benserazid (a peripheral decarboxylase inhibitor), dose ratio 4:1). Each treatment phase lasted for 8 weeks. Modapar was found to be significantly superior to CB 154 in the treatment of the Parkinson state as a whole (Webster total score) and the individual symptoms of hypokinesia, rigidity and tremor. Compared with pretreatment score, CB 154 had a weak, but significant effect on tremor, but not on the Webster total score, hypokinesia and rigidity. The effect of CB 154, however, varied: four patients preferred CB 154 to Madopar on account of its satisfactory therapeutic effect and fewer side-effects ("on-off" phenomena, hyperkinesia, psychiatric complications); other patients showed neither therapeutic effect nor side-effects of CB 154, which in some cases may be related to too low a dose-level of CB 154 (median 30 mg daily, range 20-60 mg). In the four cases first mentioned which showed a good effect of CB 154, the ratio between the dose of CB 154 and the dose of L-Dopa (in Madopar) was 3.5-10 mg/100 mg, i.e. in certain cases it must be assumed that the maximum dose of CB 154 lies around 120 mg daily.