The ratio of dry weight to wet weight of infected snails (5.5 +/- 2.2%) is significantly smaller than that of uninfected animals (8.3 +/- 1.0%). 2. The specific values of oxygen consumption and heat-production per dry weight are significantly higher for infected snails (2.41 +/- 0.44 microliter O2/h/mg; 12.63 +/- 1.24 muW/mg) than for uninfected ones (1.88 +/- 0.24 microliter O2/h/mg, 8.94 +/- 0.91 muW/mg). 3. The rate of oxygen consumption always suffices to explain the measured heat flows for aerobic catabolism of carbohydrates or fats and proteins, respectively. Neither for infected nor for uninfected snails is it necessary to assume an anaerobic energy metabolism. 4. Structures in the calorimetrically obtained heat production curves are discussed.