Rosmarinus officinalis is widely found in the lands of Aegean and Mediterranean regions of Turkey. Stem explants of very young shoots were cultured in both woody plant medium (WPM) and Murashige and Skoog (MS) media supplemented with 7 g/L agar, 30 g/L sucrose, and 1 and 3 mg/L naphthaleneacetic acid (NAA) for callus initiation. Induced calli were subcultured 4 times with intervals of 7-10 days. MS medium supplemented with 1 mg/L NAA proved to be the best medium for the production of callus (65.0%) among the samples tested. The lyophilized calli were subjected to solvent extraction. Active constituents of 8 calli extracts were analyzed by HPLC, and rosmarinic acid (RA) was determined to be the primary compound. Calli cultivated in WPM supplemented with 1 mg/L NAA and extracted at 50 degrees C, yielded the highest amount of RA (34.4mg/g dry weight). Moreover, antioxidant activity of calli extracts was determined using a number of in vitro assays, including total phenol assay, DPPH radical. scavenging activity (RSA), and trolox equivalent antioxidant capacity (TEAC). On the basis of the current findings, we conclude that WPM supplemented with 1 mg/L NAA yields higher phenolic content as well. as higher antioxidant activity. (C) 2007 Elsevier GmbH. All rights reserved.