We examined the role of cholinergic mechanisms in causing the increase in histamine bronchial responsiveness that follows allergen exposure. Five stable adult atopic asthmatics received inhalation tests with histamine on 2 days after both placebo and a dose of atropine sulphate (18 mg nebulized during tidal breathing), which reduced saliva output. On a third day, an allergen inhalation test was carried out to stimulate a dual asthmatic response. When the FEV1 had returned to within 10% of baseline, the histamine test was repeated after placebo and atropine. Before allergen inhalation, atropine marginally increased the FEV1 (p = 0.12) and reduced bronchial responsiveness to histamine (p = 0.003). When allergen challenge had induced an increase in histamine responsiveness (p = 0.001), atropine again marginally increased FEV1 (p = 0.063) and reduced the responsiveness (p = 0.004) but did not return the responsiveness to the preallergen level (p = 0.023). There was no evidence that the magnitude of the atropine blockade of histamine responsiveness was different before and after allergen (p = 0.92). We conclude that cholinergic mechanisms are not likely to explain the increase in bronchial responsiveness that follows allergen-induced inflammation.