Eosinophilia-myalgia syndrome (EMS) is an alarming illness, occasionally fatal, which is characterised by severe myalgia, arthralgia, fatigue and, it now appears, ingestion of L-tryptophan (Hertzman et al, 1990). At first sight this appears rather surprising because tryptophan is, of course, present in the normal diet, albeit in smaller quantities (about 750 mg daily), than that usually prescribed for the treatment of depression (about 3 g daily). Furthermore, L-tryptophan has been available in the UK for the treatment of depression for over 20 years without previous cases of EMS coming to light, despite the dramatic nature of the symptomatology. All this suggests that a contaminant in the preparation of synthetic L-tryptophan could be responsible for the development of EMS, a view strengthened by the resemblance of EMS to the toxic oil syndrome which was caused by contaminated olive oil.