The supercritical fluid extraction (SFE) of aroma compounds from Thyme (Thymus zygis L. subsp. sylvestris) was studied. Extraction was conducted at different temperatures (300-323 K) and pressures (8-20 MPa). The extraction time was varied between 40 and 100 min. The study was carried out according to the response surface methodology (RSM). The extracts were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The yield and the composition of the extracts obtained by supercritical CO, were compared with those obtained by steam distillation (SD). SFE produced higher extraction yields than SD. This may be explained by simultaneous extraction of both aroma and non aroma compounds of higher molecular weight. Higher yields were produced for the higher Values of pressure (20 MPa) and extraction time (120 min). With respect to extract composition, the content of hydrocarbon monoterpenes was shown to be mainly related to the extraction temperature, higher values being produced between 308 and 310 K. Phenols, including thymol, the major component of T. zygis aroma, were also extracted at the higher tested levels of the parameters. The production of the terpenic alcohols (TA) was found to be mainly dependent on the extraction time. This study allows the conclusion that pressure is the most important extraction parameter. (C) 2000 Elsevier Science B.V. All rights reserved.