Chlorophylls and carotenoids were extracted from leaves of stinging nettle (Urtica dioica L.) with supercritical and liquid CO2. The solvent modified with ethanol (0-7 wt.%) was applied at the pressures of 200, 250 and 280 bar and the temperatures of 25, 40 and 60degreesC. Extracts were analysed by means of HPLC and RP-HPLC methods. The maximum yields of chlorophyll a, chlorophyll b, beta-carotene and lutein obtained with CO2 were 73, 100, 24 and 39 mg/100 g dry matter, respectively. In comparison with the extract obtained using conventional solvents, the maximum yields obtained with CO2 were similar for carotenoids, higher for chlorophyll b and lower for chlorophyll a. Chlorophyll a partially degraded in the extractor to the more soluble pheophytin a; the extent of carotenoid degradation was much lower than that of chlorophylls. The degradation was substantially reduced by addition of a small amount of antioxidant to the solvent. Extraction rates in dependence on extraction conditions were measured both for individual pigments and for oleoresin. A model describing the extraction of a solute that is present in two forms, free and interacting with matrix, was applied to interpret the experimental extraction curves. A loss of volatile substances from the ground nettle leaves and a decrease in beta-carotene content from 24 to 18 mg/100 g dry matter was observed during the period of 155 days between the first and last experimental run. (C) 2003 Elsevier B.V. All rights reserved.