A miniaturized calorimeter, based on silicon integrated thermopile chips, has been developed for the determination of growth-related heat production in microbial cultures. The calorimetric vessels consists of two independent sensors located within a thermostated aluminum frame, the heat sink, and covered by a 0.6ml reaction chamber made of PTFE for improved thermal insulation. The second sensor was used as a reference to minimize temperature perturbations on the output signal. Baseline stability was better than 0.08 muW h(-1). The Si thin-film membrane which supports the Al-Si thermopiles enabled an excellent dynamic response and a temperature resolution of 50 muK. The sensitivity for the heat power measurement was 0.39 V W-1. Batch measurements of Escherichia coli activity under different conditions have been performed. The thermal profiles matched the exponential growth kinetics usually found in batch cultures of bacteria. A simplified model based in the Monod equation is used to analyze the influence of oxygen depletion on cell growth. (C) 2004 Elsevier B.V. All rights reserved.