The relationship between occupational asthma (OA) and non-specific bronchial responsiveness (NSBR) is reviewed. Natural or laboratory exposure to ubiquitous allergens can induce or increase NSBR. Reduction of exposure has an opposite effect. Preliminary results suggest that NSBR is not a predisposing factor to OA. NSBR assessment can be useful in screening for OA, before employment to document baseline levels and serially afterwards, alone or combined to immediate skin reactivity to the occupational agent, to document the onset of OA. Showing NSBR is essential to the diagnosis of OA. Although specific broncho-provocation tests in a hospital laboratory still represent the gold standard to confirm OA, the demonstration of changes in peak expiratory flow rates, in particular if such changes are coupled to NSBR, is an important diagnostic tool. NSBR assessment is also an interesting guide to specific bronchoprovocation in the laboratory. Several studies have documented a reduction in NSBR in some cases of OA after removal from exposure to the causal agent. The degree of NSBR is one of the criteria that have been suggested in setting permanent disability in subjects with OA. Increased NSBR can exist in other occupational conditions and represents an essential feature of Reactive Airways Dysfunction Syndrome (RADS).