1. Seneciphylline, one of the hepatotoxic pyrolizidine alkaloids, can induce a marked arterial and arteriolar hypertrophy of the lung of young Wistar rats a month after a single s. c. injection of 50–80 mg/kg.
2. Seneciphylline and senkirkine, two pyrrolizidine alkaloids, have mutagenic activity in Drosophila and their transfer into rat milk.
3. Seneciphylline can significantly increased the activities of epoxide hydrase and glutathione-S-transferase but cause reduction of cytochrome P-450 and related monooxygenase activities.