In 1989 more than 1500 people who took the dietary supplement L-tryptophan for insomnia and depression developed eosinophilia myalgia syndrome (EMS)-a potentially fatal disease characterized by an excess of a type of white blood cell called eosinophils. Disease symptoms include fever, muscle aches and inflammation, and skin rashes. As many as 40 of the patients who became ill died. It is suspected that impurities in the supplements caused the disease. More recently, similar impurities have been detected in batches of a similar dietary supplement called L-5-hydroxytryptophan.