Methacholine testing is an important diagnostic tool for asthma. Newly available dosimeter and software technology allows for simplification of the test. This study aimed to evaluate a single-concentration dosimeter protocol for methacholine testing by comparison with a multi-concentration dosimeter protocol similar to that recommended by the American Thoracic Society (ATS) (standard protocol). Fifty young subjects with high pretest probability for bronchial hyperresponsiveness underwent two challenges in randomized order within one week. The novel protocol used a Medic-Aid Sidestream nebulizer and a fixed methacholine concentration of 16mg/mL. Number and duration of nebulizations were matched to the last four doses of the standard protocol, and results were expressed cumulatively. The rank correlation between log slopes (n=50) was 0.86; that between log provocative doses (n=18), which differed at low values, was 0.58. When requiring a 20% fall in FEV(1) at any methacholine dose, 18 subjects were hyperresponsive and 28 normoresponsive in both tests (46/50 concordant). One subject was positive only with the standard, and 3 only with the novel protocol (Cohen's kappa 83%). The novel protocol for methacholine testing yielded qualitative results similar to those of the ATS multi-concentration protocol, although there were quantitative differences at low doses. However, its design and handling may offer advantages for clinical practice.