Hypericum perforatum is a medicinal plant that has been known in traditional medicine as an anti-inflamatory and healing agent. The alcoholic extract of its aerial parts finds wide application for its antidepressant activity. Three methods of extraction into 80% ethanol were compared. An HPLC method with fluorimetric detection was developed for the identification of its constituents. The calibration curve was strictly linear in the concentration range from 0.1 to 10 µg.cm^-3 of hypericin with the correlation coefficient r > 0.999 and the detection limit (LOD for 3 S/N) 0.006 µg.cm^-3. HPLC with fluorimetric detection can separate and detect naphthodianthrone derivatives in Hypericum perforatum in the presence of other constituents with a greater specificity than HPLC with spectrophotometric detection at 592 nm. Hypericin was quantified in the culture tissues of Hypericum perforatum L. var. Topaz cultivated under different conditions (saccharose and antibiotics concentrations) in the Murashige - Skoog medium.