Cell-free extracts of Ruta graveolens cell suspension cultures obtained after (NH 4 ) 2 SO 4 precipitation and gel filtration on Sephadex G-25 catalyze the condensation of N-methylanthranilic acid and malonyl-CoA in the presence of ATP. The reaction product has been identified as 1,3-dihydroxy-N-methylacridone. This alkaloid 6 is apparently the key intermediate in the pathway leading to more complex acridone alkaloids.