Validation of test-shortening procedures for the 2-min tidal breathing methacholine challenge method.Retrospective chart review.Tertiary-care university clinical pulmonary function laboratory.One thousand subjects aged 10 to 85 years (mean +/- SD, 44.5 +/- 16.0 years), 44.5% male, referred for methacholine challenge.Two-minute tidal breathing methacholine challenge was performed, with both physician and technician access to published test-shortening procedures.There were 315 positive test results (provocative concentration of methacholine causing a 20% fall in FEV(1) [PC(20)] or = 20% FEV(1) fall on the first inhalation, and 11 subjects had a > or = 20% FEV(1) fall after a skipped concentration. In only one case (0.1%) an FEV(1) fall > or = 40% on the first concentration was reported, compared with no cases after a skipped concentration and seven cases with a > or = 40% FEV(1) fall after a routine doubling dose step-up.The 2-min tidal breathing methacholine test in clinical practice can be safely shortened to an average of less than four inhalations using starting concentrations based on FEV(1), asthma medication, and clinical features, and by occasionally omitting concentrations.