L-tryptophan associated eosinophilia-myalgia syndrome. Environmental chemicals are increasingly incriminated in the pathogenesis of several disease states. The eosinophilia-myalgia syndrome is a recently described entity attributed to the ingestion of the normal dietary amino acid L-tryptophan. We describe a patient who fulfills criteria for the eosinophilia-myalgia syndrome and who was ingesting supplemental L-tryptophan. Exhaustive investigations failed to reveal other causes for her eosinophilia or her myalgic/neuropathic complaints, and she improved dramatically when she discontinued the L-tryptophan supplements. The mechanisms whereby this chemical may induce this syndrome are discussed. 