Calorimeters are normally calibrated electrically. In the case of isothermal microcalorimeters the heat flow pattern in electrical calibration experiments are in some cases significantly different from that of investigated processes which may lead to important systematic errors. Ln such cases use of chemical calibration methods should be considered. It is of general importance to conduct tests of the performance of calorimeters using well established chemical test processes. References are given to some chemical test and calibration processes for isothermal microcalorimetry conducted under ambient conditions.