β Epidemiological surveys on Parkinson's disease that have been carried out in different parts of the world have suggested that the disease is uniformly distributed in white populations. The position with regard to the Mediterranean peoples is still controversial, because of the large variation of the frequencies observed in the different areas that have been investigated. We therefore studied the frequency of Parkinson's disease in the Local Health Service of Ferrara, northeastern Italy (mean population, 187 000). Based on 394 patients, the mean incidence per year for the period from 1967 through 1987 was 10.01/100 000. The incidence rate of Parkinson's disease among cases with early onset was found to be statistically higher in rural areas as compared with urban ones (6.32/100000 vs 3.11/100000). Moreover, the study revealed a significantly higher incidence rate among agricultural workers (20.6/100 000). These results would seem to give further support to the hypothesis of a possible causal role of environmental factors that are mainly linked to agriculture, most likely due to the continual exposure to toxic agents in this area. However, further studies, which are not exclusively epidemiological, are necessary before any conclusions may be drawn, because many confounding variables may account for the results from surveys of this type.