The etiology of adult-onset asthma is incompletely understood. High-intensity exposure to irritants is one accepted risk factor and such cases are termed Reactive Airways Dysfunction Syndrome. The contribution to asthma of less intense and less acute exposure to irritants remains to be clarified. We report on 10 cases of nonsensitization adult-onset asthma in settings of exposure to noticeable but distinctly "tolerable" levels of inhalation irritants. This series of 10 cases represent 31% of verified asthma cases seen in our environmental and occupational medicine referral clinic over a 5-year period. We believe further exploration of this phenomenon of low dose Reactive Airways Dysfunction Syndrome is warranted.