In 65 asthmatic patients aged 18 to 59 years maximal expiratory flow-volume curves were performed. The measurements were done with a pneumotachograph in connection with a self-developed two-channel FM modulator, a stereo tape recorder, and a X-Y recorder. We examined 53 patients in clinical remission and 12 patients during an attack period. The greatest sensitivity of the tested flow-volume data had MEF 50/FVC pred. and the time constant of the terminal portion of the curve. MEF 50/MEF 75 and V2/V1 were about equally sensitive for detecting ventilatory inhomogeneities. The attack group most differed from the remission groups in FVC % pred., MEF 50/FVC pred. and the other flow rates. The flow-volume curve is a valuable method to assess obstruction and ventilatory inhomogeneity in asthmatic patients. It has a greater sensitivity than conventional spirometry.