We have investigated the possibility that a bronchoconstriction accompanies the vagally-mediated bradycardia induced in man by immersion of the face in cold water. Forced expiratory flows (FEF) at 40% and 25% of vital capacity (VC) have been measured from partial flow-volume curves obtained during forced expirations starting at 70% VC. These were performed immediately after 15 s apnoea with or without face immersion, and compared with control expirations having the same volume history but without the preceding apnoea. Five of the 10 subjects showed evidence of a greater than 10% reduction in FEF, which averaged 17% (Fig. 2). Half the response was attributable to the apnoea alone and the other half, which was abolished by ipratropium, to cold face immersion (Fig. 3). This bronchoconstriction appears to be a new component of the 'diving response' in man, mediated, like the bradycardia, by vagal efferents.