OBJECTIVE: To investigate the risk of enzyme sensitisation and clinical allergy in workers exposed to enzymes at Novo Nordisk A/S. METHODS: The study was a retrospective follow up study based on medical history and test data originally collected at routine screenings for enzyme allergy by the Occupational Health Service (OHS) of Novo Nordisk A/S during the period 1970-92. Workers were exposed to proteases, lipases, cellulases, and carboxyhydrases. Medical records of 3815 subjects were registered in the OHS database. According to criteria including possible enzyme exposure, allergy tests at the time of engagement, and participation in the allergy screening programme 1064 were selected for the present study. Outcomes were allergy symptoms, specific IgE test (radioallergosorbent test (RAST)) to enzymes, skin test reactions to common allergens and enzymes, forced expiratory volume in one second (FEV1), and forced vital capacity (FVC). Potential risk factors were smoking habits, workplace, type of job, age, and sex. RESULTS: Sensitisation occurred to all types of enzymes handled in the plant, most often in production areas and laboratories; 8.8% developed clinical enzyme allergy during the first three years of employment. The risk declined during the period. The frequency of enzyme sensitisation, expressed as RAST values > 0.5 SU, was 36%, and the frequency of significant RAST values > or = 2 SU was 8%. Ranking diagnoses of enzyme allergy by severity, the frequency of asthma was 5.3%, rhinitis 3.0%, and urticaria 0.6%. Half of the cases occurred within the first 15 months of exposure. Smoking was an independent risk factor for clinical enzyme allergy (odds ratio (OR) = 2.3 (95% exact confidence interval (95% CI) 1.4 to 3.9), measurable RAST > or = 0.5 SU (OR = 1.5 (95% CI 1.1 to 2.1)), and RAST > or = 2 SU (OR = 4.5 (95% CI 2.2 to 8.4)). Atopic predisposition at the time of engagement was not a significant risk factor for enzyme allergy. This could be due to various selection mechanisms.