Cell suspension cultures of the hornwort Anthoceros agrestis Paton (Anthocerotaceae) were cultivated and characterized in CB-media containing 2 and 4% sucrose. The suspension cells accumulated rosmarinic acid up to 5.1% of the cell dry weight as well as caffeoyl-4'-hydroxyphenyllactate. Moreover, a more hydrophilic compound was detected which was isolated and identified as rosmarinic acid 3'-O-beta-D-glucoside, a new rosmarinic acid derivative. This new rosmarinic acid derivative was found up to 1.0% of the cell dry weight in suspension cells of A. agrestis.