Plant secondary compounds can have stimulating effect on C cycling and change its rate in soils. We examined how leaves of bay laurel (Laurus nobilis L.; Lauraceae) and 1,8-cineole (CIN), one of its constituents, affect soil C mineralization and its rate. Leaves and soil samples of bay laurel were taken from Cukurova University Campus (Adana, Turkey) growing naturally under Mediterranean climate conditions. Leaves and CIN were considered as the two forms of organic C sources. After determining the level of 1,8-cineole in leaves by gas chromatography-mass spectrometry, soils were mixed with powdered leaves and 1,8-cineole based on their C contents at same and half doses of soil organic C level. Carbon mineralization of all soils was determined over 54 d (28 degrees C, 80% field capacity). While 1,8-cineole was found as a major constituent of leaves (65% of essential oil), all doses of leaves and CIN increased soil microbial activity. There were significant differences for C mineralization rate between control and all applications (P < 0.05). High C levels of all treatments decreased C mineralization rate compared to control soils. In summary, all treatments stimulated C mineralization and it is possible to conclude that soil microorganisms adapted to use CIN as an energy source.