Parkinson*s disease is a common degenerative disease that causes rigidity, bradykinesia and rest tremor in patients. Available treatments include levodopa (the major drug) and other supplementary drugs (bromocriptine or SELEGILINE) which can reduce such disabilities, but because of the necessity of their uses for a long term treatment, many side effects are being expected. Thus, due to lack of sufficient reports about efficacy and side effects of such supplementary drugs, this experimental study was carried out.Seventy seven patients (50 men and 27 women) with the average age of 68±8.42 years were divided into three groups. In group A, levodopa and trihexyphenidyl (Artan®) were administered to 18 patients. In group B, SELEGILINE (Deprenyl®) was used as a supplementary and was administered with levodopa and trihexyphenidyl for 25 patients. In group C, bromocriptine was used in place of SELEGILINE, for 34 patients.In a three year period, the patients were followed up, in conformity with UPDRS (Unified Parkinson*s Disease Rate Scale). In this experimental study, group C showed better physical activities in comparison with group A and group B, in spite of having better conditions at the first year showed totally little differences in comparison with group A. With a view to side effect particularly dyskinesia; there was little side effect in group C. On the basis of results of this investigation it appears that bromocriptine as a supplementary drug in comarison to SELEGILINE has fewer side effects.