The potential of cell suspension and ‘hairy root’ cultures of horseradish for production of peroxidase was assessed and the factors limiting production in culture were examined. Peroxidase activity is closely related to growth in both cell suspension cultures and ‘hairy root’ cultures of horseradish. Under the growth conditions used in the present study however, cell suspension cultures produce twice the total activity of ‘hairy root’ cultures, and up to 8% of this activity is released into the culture filtrate at high specific activity. The growth and peroxidase activity of cell suspension cultures are limited by both phosphate and sucrose and the rate of oxygenation of the culture is critical for maximising growth rate, biomass accumulation and peroxidase activity. The isoelectric focussing banding pattern of peroxidase from the ‘hairy root’ cultures was identical with commercially available horseradish peroxidase whilst that from cell suspension cultures differed with an additional two bands at high pI.