This report describes three Belgian cases of the eosinophilia-myalgia syndrome associated with the use of L-tryptophan-containing products. Three women, aged 51, 53 and 73 years, were taking L-tryptophan for 2 months to 2 years, at 500, 1500, and 2250 mg d-1, respectively. All developed disabling myalgias, fatigue, and a variable skin rash, in association with marked eosinophilia. In one patient, symptoms and eosinophilia reappeared after rechallenge with L-tryptophan. Discontinuation of the drug resulted in gradual disappearance of the symptoms, signs and laboratory abnormalities in two patients. One patient was treated with corticosteroids because of persisting myalgias. Because of the non-specific clinical manifestations, clinicians from all subspecialties of internal medicine might be confronted with such patients and should be aware of this new entity.