In the past decades knowledge of respiratory physiology of cetaceans and other marine mammals has reached a level in which we are able to understand much of the adaptive mechanisms which these creatures need to survive in an aquatic environment. However, in vivo spirometric data of dolphins are scarce and incomplete. Spirometry in dolphins could increase our knowledge and understanding of the ventilatory system and its response to several events, such as growth, various diving activities, stress and disease. Furthermore, spirometry could be a useful tool in examining the integrity of the respiratory system and picking up signs of disease at an early stage in a non-invasive manner. Adding other measurements to the spirometric findings could further increase the diagnostic yield. Such measurements might be capnography, oxygen consumption and measurement of inflammatory parameters in exhaled gas. Lung function measurements are non-invasive and little stressful to the animals and can therefore be repeated as often as necessary. They can be applied both as screening and as diagnostic tool. Because of the very short duration of a breath cycle in combination with very high airflows, spirometry in dolphins is technically challenging. Spirometry was performed with a Masterscope modified pneumotach for animals, VIASYS Healthcare GmbH, Hochberg, Germany, sample frequency 0.5 kHz, R = 36 Pa/L/s. A especially for this purpose designed mask connected to a hose (8 cm diameter) was put over the blowhole to which the pneumotach was connected. Two flow-volume curves for the largest of the three dolphins measured will be shown and discussed. For comparison also the maximal flow-volume curve of a normal human adult is sketched. As can be seen the peak expiratory flow rate is about 80 litres/sec (almost ten-fold higher than that of a human). The linear decrease in flow during a forced expiration as seen by humans is absent in dolphins Expiration time was only 0.33 sec so a FEV1 can not be determined. Inspiration took 0.78 sec and shows a peakflow of about 28 litres/second. Both curves (as well as all the other curves measured) show a pattern of inspiratory flow limitation / constant inspiration flow speed. The inspiratory vital capacity was 17.3 litre. Between the two breaths there was a 19 seconds breath-hold period. The two other smaller dolphins showed similar shaped flow-volume curves (having a VC of respectively 9.5 and 8.1 litres). Further measurements will be performed, but these results show that in this manner spirometry is feasible in dolphins.