The supercritical CO2 extraction of lemon balm (Melissa officinalis, L.) at pressures from 10 to 18 MPa and at temperatures of 308-313 K was studied. The antioxidant activity of lemon balm extracts, obtained from solid residues of supercritical extraction and from raw lemon balm leaves, was performed using the Rancimat method. The best protection factor curve was obtained when extracts from the solid residues of supercritical extraction at 10 MPa, 308 K and 4 h of extraction time were used. A spectrophotometric method was used for the determination of the polyphenol compounds in the extraction residues. The highest value of phenol compounds was obtained for the extracts of solid residues of supercritical extraction at 10 MPa, 323 K and 30 min. (C) 2001 Elsevier Science B.V. All rights reserved.