Occupational exposures now account for 20% of adult onset asthma. Overall incidence has not declined, but recognition of the problem and substitutions have resulted in dramatic reductions in some causes of occupational asthma, particularly latex and glutaraldehyde in healthcare workers. Newer at risk workers include cleaners and those exposed to metal-working fluid. Standards of care have now been published, supported by evidence- based reviews of the literature, which are likely to require referral to centres specialising in occupational asthma for compliance. The spectrum of occupational asthma is expanding, with low-dose irritant mechanisms likely to account for some occupational asthma with latency. Eosinophilic and non-eosinophilic phenotypes are also seen, the non-eosinophilic variant having more normal non-specific responsiveness than the eosinophilic subgroup. Physiological confirmation of occupational asthma is required but remains challenging. Specific challenges may be negative in workers confirmed as having occupational asthma from workplace challenges. Serial measurements of peak expiratory flow or FEV1 are feasible in the occupational health and general respiratory clinic settings and provide a method of validation of occupational asthma in those without ready access to specific challenge testing, while minimum data quantity standards are now established which need to be achieved for optimal sensitivity/specificity. New developments in the analysis of serial mea-surements of peak expiratory flow comparing the mean hourly values on work and rest days have shown good specificity and sensitivity from shorter records (but more frequent readings) than needed for the standard Oasys score.