A novel bench-scale calorimeter, which is based on a heat-flux principle and modified to accommodate biol. reactions, was evaluated for detg. the heat evolution rate of an aerobic culture of the yeast Kluyveromyces fragilis grown on lactose. The instantaneous heat evolution rate was an accurate indicator for the instantaneous overall metabolic activity. On the other hand, the integrated heat prodn. increased in parallel to the accumulated cell dry wt. The ratios of heat generated per g biomass produced and of heat generated per mol of consumed O were const. throughout the expt. despite changing growth rates and metab. [on SciFinder (R)]