Plant cell cultures of Peganum harmala converted geranyl acetate to geraniol. Although the reaction started immediately after feeding, there was disappearance of both product and substrate. Geranyl acetate at 100 mg l(-1) when fed to 100 ml Peganum harmala suspensions (16% packed cell volume) was completely used within 24 h without accumulation of any product. Similarly, linalyl acetate and its biotransformation products, linalool and alpha-terpineol, disappeared. Controlled-release polymer discs made from poly-2-hydroxyethyl methacrylate and containing concentrations of geranyl acetate or linalyl acetate produced greatly extended concentrations of these substrates and their biotransformation products (from about 1 day to over 12 days). The concentrations of substrates remained at around 5 mg l(-1) throughout the experiments, while the concentrations of biotransformation products increased from 10 mg l(-1) to 55.5 mg l(-1) for geraniol, from 5 mg l(-1) to 14 mg l(-1) for linalool, and 5 mg l(-1) to 12 mg l(-1) for alpha-terpineol compared to the control value. Also low concentrations (30-200 mu g/disc) of product were taken up by the polymer over 10 days.