Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand activated transcription factor, belonging to the metazoan family of nuclear hormone receptors. Activation of PPARgamma increases the transcription of enzymes involved in primary metabolism, leading to lower blood levels of fatty acids and glucose. Hence, PPARgamma represents the major target for the glitazone type of drugs currently being used clinically for the treatment of type 2 diabetes. Furthermore, activators of PPARgamma show beneficial anti-inflammatory and anti-tumour effects. Utilizing a fusion receptor of the yeast Gal4-DNA binding domain joined to the hinge region and ligand binding domain of the human PPARgamma in combination with a Gal4-driven luciferase reporter gene, cotransfected into Cos7 cells, we tested sage and rosemary extracts prepared with 80 % aqueous ethanol for possible PPARgamma activation. This revealed that both extracts are capable of selectively activating Gal4-PPARgamma fusion receptor, in a concentration-dependent manner, with EC (50) values of 22.8 +/- 8.4 mg/L and 33.7 +/- 7.3 mg/L for rosemary and sage, respectively. Subsequent analysis of the characteristic constituents revealed the phenolic diterpene compounds carnosol, present in both herbs, and carnosic acid to be active principles of these extracts, showing EC (50) values of 41.2 +/- 5.9 microM and 19.6 +/- 2.0 microM, respectively. Thus it can be concluded that the glucose lowering effect reported recently for rosemary may be attributed to PPARgamma activation. Moreover, our observations may also explain the anti-inflammatory and antiproliferative effects of both compounds published previously.