RESUMEN
In January and February 1987 an epidemic of a strange illness involving 31 members of the staff in the Calcutta Telephone Exchange occurred. It commenced in the "operator services" on the 4th floor and after involving 21 members of the staff, progressed to the 6th floor where a further 10 members of the staff were involved. The symptoms varied and included a burning feeling on the face, weakness of the limbs, noises in the ear and heaviness of the head. In most cases no physical injury was found and a psychological disorder occurred subsequently in a few cases. Extensive investigation of the network did not reveal any specific electronic causes although some defects were found. The likely causative factors were poor ventilation causing a mild excess of CO2 as well as a mild heat load, overlaid on a background of work stress. The epidemic was exacerbated by erroneous reports in the media and by rumour that the members of the staff admitted to hospital were permanently injured. The epidemic abated in conjunction with steps to improve the work environment and to improve medical communication. The epidemic is discussed with regard to mass sociogenic illness.