Clinical data demonstrate that there is a significant difference between at least two types of idiopathic Parkinsonian patients; a benign type of Parkinson's disease and a malignant type. They can be distinguished by the time course of a disability-score, independent of the duration of the disease. The benign cases respond very well to L-Dopa (Madopar) treatment and show a long lasting (7 years) drop in the disability, whereas the improvement of disability in the malignant cases is much smaller and lasts for about one year, followed by an increase of disability. The duration of the disease is 12,5 +/- 0,4 years in the benign type but only 4,0 +/- 0,3 years in the malignant type. Akinetic crises, off-phases, hyperkinetic crises and toxic deliria after Madopar treatment can be observed later in the benign than in the malignant cases. These results suggest that the degeneration of the dopaminergic nigrostriatal system occurs much more rapidly in malignant cases than in benign cases of Parkinson's disease.