Occupational type bronchial provocation testing first requires satisfactory control data, in particular stable values for FEV1 for 10-12 hours. In this case regular beclomethasone, salbutamol, and ipratropium were needed to achieve baseline stability. Such treatment may block asthmatic reactions, but in practice larger exposures can usually overcome any protective effect of these drugs. The initial bronchial provocation tests were with components of hard metal, the only recognised cause of occupational asthma in grinders, drillers, and cutters. Tungsten carbide (which is thought to be inert) was used as the control for cobalt, which is responsible for occupational asthma in hard metal workers. There was no reaction to either exposure.