The effects of deep inspiration upon expiratory flow rates and response to inhaled metaproterenol were studied in normal and asthmatic subjects using partial (PEFV) and maximal (MEFV) expiratory flow volume curves. Routine pulmonary function tests and specific conductance were also measured. Prior to administration of metaproterenol, 18 of 24 normal subjects and 11 of 24 asthmatic subjects (p 0.05) had higher flow rates on MEFV than on PEFV curves. The 11 volume history responsive asthmatic subjects showed better lung function and more density-dependence of expiratory flow than the other 13 asthmatic subjects; furthermore, the effect of lung inflation was significantly larger in the volume history responsive asthmatic subjects than in the volume history responsive normal subjects. Responses to inhaled metaproterenol were much larger on PEFV than MEFV curves; nevertheless, differences between normal and asthmatic subjects in metaproterenol responsiveness were less using PEFV curves. Thus, the use of PEFV curve measurement did not facilitate the detection of individual asthmatic responses to inhaled metaproterenol.