The methanol extracts of the aerial parts of Hypericum mysorense and Hypericum patulum were tested for in vitro cytotoxicity on HEp-2, RD and Vero cell lines and antitumour activity using DLA and HEp-2 cell lines. The cell viability and morphological changes were assessed. Of these extracts, Hypericum patulum (stem) extract showed strong cytotoxicity against all the cell lines used. The CTC50 of the Hypericum patulum (stem) extract was 1.71 µg/mL for HEp-2, 1.53 µg/mL for RD and 2.23 µg/mL for Vero cell lines. The Hypericum patulum (leaves) and Hypericum mysorense (aerial parts) extracts showed moderate cytotoxicity and Hypericum patulum (aerial parts) extract did not show any cytotoxicity up to 1000 µg/mL concentration. In the clonogenic assay, no colony formation was observed at a concentration of 300 µg/mL and above for Hypericum mysorense (aerial parts), 400 µg/mL and above for Hypericum patulum (leaves) and 500 µg/mL and above for Hypericum patulum (stem) extracts. In the short term antitumour studies using DLA cells, 50% viability was observed in the concentration range 100–200 µg/mL for Hypericum patulum (leaves and stem) and 200–400 µg/mL for Hypericum mysorense (aerial) extract. In the long term antitumour activity using the HEp-2 cell line, no colony formation was observed over a concentration of 1.6 µg/mL for the Hypericum patulum (stem) extract. Copyright © 2003 John Wiley & Sons, Ltd.