An improved flow-through chip calorimeter useful for liquid samples is presented. The heat power detection limit could be decreased to a level of 180 nW. Main features of the new micro-sized calorimeter are a differential chip arrangement, a small sized thermostat with a precision in the micro-kelvin range and the application of micro-pumps for liquid flow control. The improved heat power resolution enables the monitoring of biochemical processes under relevant conditions. As applications have shown a pulsed fluid injection can increase the degree of mixing. For the determination of the degree of mixing a new method was developed. (C) 2003 Elsevier B.V. All rights reserved.