A retrospective study on occupational rhinitis and asthma diagnosed in 7 occupational health institutes in Lombardia (North-West Italy) was performed using a standardized card. 141 cases of rhinitis and 281 cases of asthma due to sensitization to occupational agents were analyzed and their clinical characteristics, aetiology, diagnostic methods and associated allergic diseases were determined. In this population the most frequent agents of occupational rhinitis were wheat flour and latex, whereas those of occupational asthma were latex and isocyanate. More than half of the subjects had more than one clinical manifestation of allergy. In 92 out of the 281 asthmatic patients rhinitis was the first clinical manifestation, particularly in subjects sensitized to high molecular weight substances, and preceded, asthma by 12 months as a mean. Specific bronchial provocation tests were useful for the diagnosis of asthma in 153 of the asthmatic patients and 45 of them had an isolated late bronchial reaction following the specific stimulus. At diagnosis 61 subjects (21.7%) had FEV1 < 80% of predicted; factors associated to ventilatory impairment were sensitization to high molecular weight substances, duration of exposure to the sensitizing agent, persistence of exposure after onset of symptoms.