Researchers investigating the genetic component of various disease states rely increasingly on murine models. We have developed a ventilator to simplify respiratory research in small animals down to murine size. The new ventilator provides constant-flow inflation and tidal volume delivery independent of respiratory parameter changes. The inclusion of end-inspiratory and end-expiratory pauses simplifies the measurement of airway resistance and compliance and allows the detection of dynamic hyperinflation (auto-positive end-expiratory pressure). After bench testing, we performed intravenous methacholine challenge on two strains of mice (A/J and C57bl/bj) known to differ in their responses by using the new ventilator. Dynamic hyperinflation and a decrease in compliance developed during methacholine challenge whenever respiratory rates of 60–120 breaths/min were employed. In contrast, if dynamic hyperinflation was prevented by lengthening expiratory time, (respiratory rate = 20 breaths/min), static compliance remained constant. More importantly, the coefficient of variation of the results decreased when lung volume shifts were prevented. In conclusion, airway challenge studies have greater precision when dynamic hyperinflation is prevented.