Propolis or bee-glue is the third important product of honey bees after honey and wax. Known for thousands of years for its curative effects it is finding evermore attention in alternative and classical therapy in recent times against, e.g. infections, inflammations, dermatologic diseases and in wound healing. Microcalorimetric experiments were performed on the influence of several propolis samples from Germany, Uruguay, Ethiopia and of a commercial propolis tincture on growth and metabolism of the recommended gram-positive bacterium Micrococcus luteus. Propolis extracts were prepared following established recipies for the water-soluble and insoluble components and the precipitate. Addition of these extracts to a growing M. luteus culture in different growth phases resulted in a strong decline of the heat production rate, a prolongation of the lag phase or an introduction of a new, second lag phase, while the form of the calorimetric power-time curve remained unchanged. The calorimetric response showed a linear dependence on the propolis concentration. Although the quantitative gain of the extracts from the different propolis samples was nearly constant, the effects varied considerably between the specimens used. The calorimetric investigations were supplemented by polarographic oxygen monitoring and by the standard agar well technique to determine the growth inhibition factor of the propolis extracts.