An acoustic mist bioreactor which enables efficient mass transfer and higher productivity has been designed. The design is useful for cultivation of higher density biomass of hairy roots with the added advantage of simplicity in operation. In the present study Tagetes patula hairy root cultures were studied as a model system for the growth and thiophene production in this bioreactor. Results are compared with conventional designs such as bubble column and nutrient sprinkle bioreactors. Hairy roots grown in the acoustic mist bioreactor showed higher biomass (5.4 g DW 1(-1) after 15 days) and specific growth rate (0.06 per day), comparable with shake flask culture data. The specific growth rate in other designs such as bubble column and nutrient sprinkle was 0.05 and 0.05 per day, respectively. Thiophene content was maximum (2.01 mg 1(-1) after 15 days) in the acoustic mist bioreactor which was 1.4-fold greater than nutrient sprinkle and bubble column bioreactors and is close to that of shake flask level. The results demonstrate the efficacy and the advantage of the acoustic mist bioreactor for the cultivation of hairy root cultures. (c) 2003 Elsevier Ltd. All rights reserved.