The discovery that the enzymes used in biological washing powders were asthma-causing sensitizers derived initially from the concern of an industrial physician as to the possibility of pulmonary damage due to the proteolytic nature of the material. This caused a search for possible cases of enzyme-related illness. Careful history-taking led to a hypothesis concerning sensitization and allergic illness which was supported experimentally by skin prick tests and inhalation challenge tests, and later by radioallergosorbent tests (RAST). It seems that the consequences of handling this potentially allergenic material as a fine powder had not been anticipated; and failure to analyze cases of sickness, to identify asthma, and to consider its workplace source had prevented its recognition elsewhere. Contributing to this failure was the pattern of development and manifestations of allergic illness, which seldom occurred in the workplace and was not confined to enzyme workers or atopics. In some cases the incidence of illness had been suppressed, or investigation prevented.