Twelve patients with long-standing Parkinson’s disease, treated successfully with a combination of L-dopa and an inhibitor of aromatic L-amino acid decarboxylase (Ro 4–4602), in the ratio 4:1, were screened for damage to various organ systems, in particular liver and skeleton. Among other tests, liver biopsies were obtained before and after 6 months of treatment. One patient discontinued therapy because of an accentuation of pre-existent liver damage, another because of psychomental manifestations. The remaining ten patients were followed for 8–15 months and longer. The liver biopsies remained practically unaltered. Elevation of alkaline phosphatase was found in 10 out of 12 subjects. In five patients this rise fluctuated around the upper limit of normal. In two patients, who discontinued the treatment, the raised alkaline phosphatase values soon returned to normal. Analysis of isozymes proved this phosphatase to be of liver origin.All other liver function tests remained unchanged, except for an increased retention of bromsulphalein in two patients. In the one patient with the initially damaged liver, all tests became normal soon after discontinuation of therapy. No changes could be found in gastric acid secretion. All other parameters studied remained within normal limits, including urinary excretion of calcium and phos