A review, with .apprx.43 refs. A review of different types of biol. reaction calorimetry systems currently used together with the operating principles is presented. The av. resoln. of these systems is approx. 20 to 1000 mW l-1, sufficient for studies of a wide range of cell culture processes. Poorly exothermic and endothermic processes require the development of even higher resoln. systems. To this end, the Mettler-Toledo RC1 calorimeter has been extensively studied to det. the factors which limit the resoln. By changing both the hardware and software, the resoln. has been increased to 2-5 mW l-1 for non-aerated processes and to 10-15 mW l-1 for aerated systems. The changes include a switchable elec. heater for the oil circulation thermostat, a new higher resoln. A/D board, PI controller and a thermostat reactor housing. The online measurement of the power input through agitation is proposed to be essential for low heat output biol. processes, even under conditions where the rheol. properties of the culture are not believed to be changing. The results show that it is possible to develop high-resoln. systems capable of operating under std. lab. bioreactor conditions; however, it is felt that the limits to the instrument resoln. have been attained and that the calorimetric signal resoln. is limited by the requirement of high agitation, nutrient feeds, gassing, pH control and other external effects which can only be overcome by heat-balancing methods. [on SciFinder (R)]