In conventional bioreactors, the assessment of metabolic heat via heat balancing is difficult. The reason is the influence of inherent variables such as power input due to stirring, environmental heat loss and evaporation. Thus, the aim of this study is to present a newly designed chip calorimeter which can be linked to any kind of bioreactor. This chip calorimeter with a new integrated real-time sample dilution was developed and tested during batch fermentation of the bacteria Escherichia coli VH33 and the yeast Arxula adeninivorans CBS8244. The presented device is operable up to an upper limit of 4 WL-1 for the volumetric metabolic heat production rate of these biological systems. (c) 2012 Elsevier B.V. All rights reserved.