Terguride (TER) (2 mg/day) was compared with a placebo in 41 stable Parkinson's disease (PD) patients, so as to test its efficacy as an add-on treatment to spare levodopa (LD). After the 4th week of add-on treatment, LD was reduced by about 25%. The number of "stable" patients (--those with an increase of no more than 20% of the basal Columbia University Rating Scale (CURS) score--remaining after LD reduction was used to compare the two add-on treatments. Most patients, remained "stable" in spite of LD reduction, and no significant differences between the therapies were discovered; the CURS score decreased over time only in the TER group. Hence, TER was shown to be a drug that has DA-ergic properties but with minimal antiparkinsonian efficacy.