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In Reply.—
Dr Bryant has subjected our results to additional statistical analysis. His observation that disease duration correlates positively with tryptophan-associated deterioration in BPRS scores could have biological significance. The role of the serotonin system in the pathogenesis of parkinsonism remains obscure. Some evidence suggests that brain serotonergic function declines with advancing parkinsonism, possibly as a compensatory response. In this case, precursor administration might be expected to have a deleterious effect. Bryant's suggestion of possible differential effects of tryptophan on BPRS and nightmare scores may also be of interest, although the insufficiency of available data hardly invites much speculative comment. We agree that the use of tryptophan in the management of levodopa side effects should not be written off too hastily, even though our results scarcely encouraged a very optimistic view of its ultimate value.