Static and dynamic lung volumes, flow-volume curve in air and after He-O2 were carried out in 5 normal subjects baseline, immediately after rapid infusion of 2 litres of normal saline, and then 15, 30 and 60 min after. At the end of the infusion, a marked reduction of delta MEF50, FVC, FEV1, MEF50, MEF25 and an increase of Viso V and CV/VC were observed in all the subjects. The poor response to He-O2 suggests a predominant increase of small airway resistance after rapid infusion. In the recovery phase, He-O2 tests promptly returned to control values, while an increased CV/VC was detectable until 30 min after the infusion.