A CO2 laser-based photoacoustic method was used to determine the initial changes in ethylene production following emasculation of selected orchid species. The laser photoacoustic equipment consisted of a line tunable CO2 laser in conjunction with a single pass resonant acoustic cell. The minimum detection limit of the system for ethylene was 0.03 nl/1. In all tested orchid species an increase in ethylene production was measured within a few hours after emasculation. The time dependent pattern of ethylene production in Cymbidium and Oncidium showed an optimum. In Phalaenopsis and Epidendrum it was characterized by a gradual increase. The principle of photoacoustics and its application in plant physiological studies is discussed.