Background Diisocyanates are among the most frequent causes of occupational asthma in industrialized countries. Early diagnosis of diisocyanate asthma followed by prompt termination of chemical exposure can prevent chronic morbidity due to persistent asthma. The accurate diagnosis of diisocyanate asthma requires a systematic approach that combines information obtained from the occupational history, immunologic tests and physiologic studies. Methods The advantages, limitations and validity of various methods and diagnostic guidelines utilized in the evaluation of diisocyanate asthma are reviewed. Results Recommended methods for evaluation of diisocyanates asthma are similar to approaches for other causative agents. Serologic assays of speciยฎc IgE are speciยฎc but insensitive diagnostic markers of diisocyanate asthma. If possible, workers should be evaluated, while at work, in order to demonstrate work-related changes in lung function associated with diisocyanate exposures. Speciยฎc bronchoprovocation challenge testing with diisocyanates, is reserved for situations where the diagnosis cannot be conยฎrmed at work. Such tests can be performed safely but should be conducted exclusively at specialized centers by experienced personnel. Conclusions Published diagnostic guidelines for occupational asthma are directly applicable to the evaluation of diisocyanate asthma. Am.