We have studied pulmonary function before and 2 h after open sea dives to 10 and 50 m and 24 h after the dive to 10 m. Nine trainee divers participated in the dive to 10 m and 17 in the dive to 50 m. Mean time in water was 53 (32-62) min for the 10-m dive and 38 (26-76) min for the 50-m dive. Assessment of lung function included dynamic lung volumes and flows and transfer factor for carbon monoxide (TlCO). There were significant reductions (P < 0.05) in forced vital capacity of 5.8% (SD = 3.9) and 1.8% (SD = 2.8), in forced expired volume in 1 s of 6.6% (SD = 3.5) and 2.7% (SD = 2.4), in forced mid-expiratory flow rate of 10.3% (SD = 7.8) and 5.2% (SD = 6.5), and in TlCO of 11.3% (SD = 7.9) and 12.8% (SD = 5.9) 2 h after the 10- and 50-m dive, respectively. Our results indicate that factors related to submersion and increased breathing resistance contribute to changes in pulmonary function in the first hours after open-sea bounce dives.