Podophyllin, a plant derivative of variable composition, is used widely within New Zealand as a treatment for genital warts. One local source of podophyllin has been tested for ability to cause mutagenic effects in Salmonella typhimurium as well as for effects on chromosomes of Chinese hamster AA8 cells. Although only weakly mutagenic in one strain of Salmonella, podophyllin caused structural aberrations as well as changes in chromosome number in the Chinese hamster cells. The range of aberrations was similar to those caused by teniposide, a close structural relative of the major component, which was used as a positive control in the Chinese hamster cell experiments. A literature review revealed that podophyllin was shown to cause changes of chromosome number in the mouse cervix in vivo, although aberrations were not studied. Patients treated with podophyllin will usually possess one form of the papilloma virus, and this itself may have some oncogenic potential. We suggest that podophyllin could potentiate these effects and question its continued widespread use.