Energy turnover in the giant water lily, Victoria cruziana was determined by indirect calorimetry (oxygen consumption rate) and different kinds of thermometry. Experiments were performed in a greenhouse pond of the Botanical Gardens, Free University of Berlin, Germany at constant water and air temperatures (30 and 24degreesC, respectively). Flowers were investigated (i) in situ as a whole floating on the water or elevated a few centimeter above its surface, and (ii) in vitro after cutting and transporting to the laboratory: (a) as a whole or (b) dissected into their single components. Buds and flowers have heat production rates between 1 and 9 mW g(-1) wet weight, depending on their state of blooming. Results show that plant structures which are near to the floral chamber exhibit high metabolic rates and temperatures raised by about 10 K compared with outer parts like sepals. Continuous temperature monitoring reveals a time course with two heat dissipation maxima in the first evening/night and the afternoon of the second day of blooming. Growth of leaves is briefly touched.