The eosinophilia-myalgia syndrome is a newly described disease associated with ingestion of a contaminant or byproduct of the amino acid L-tryptophan. Patients typically present with intense myalgias, especially of the extremities, and commonly suffer from skin and subcutaneous manifestations (edema and induration of the skin, morphea-like lesions, pruritus). Less frequent findings are cardiorespiratory involvement (cough, dyspnea, pulmonary infiltrates) and neurologic disease (ascending polyneuropathy). Laboratory findings include blood eosinophilia (greater than 10(9) cells per liter), normal to slightly elevated serum aldolase levels, and negative studies for connective tissue diseases (normal erythrocyte sedimentation rate, negative antinuclear antibodies). Tissue damage in eosinophilia-myalgia syndrome is likely related to infiltration by eosinophils with subsequent release of toxic molecules such as major basic protein. Management in severely ill patients includes administration of corticosteroids.