Bronchial methacholine challenge is well established in asthma diagnostic and research purposes. ATS guidelines provide a short five-breath dosimeter protocol using a five-step dilution schedule. The Viasys APS system enables a feasible and less time consuming provocation with incremental dosages. In 48 young adults with bronchial hyperreactivity (BHR) the ATS-protocol with a five-step protocol using a single dilution of 16 mg/ml methacholine should be compared.