Growth of hairy roots of Tagetes patula L. was estimated by correlating biomass growth with conductivity and osmolarity changes in the medium. An inverse relationship was observed between biomass and osmolarity as well as conductivity. Osmolarity was demonstrated to be the more accurate method for the estimation of biomass. Maximum biomass was observed on the 15th day of culture period at 81.25 g (fresh wt) litre (-1) or 6.9 g (dry wt) litre (-1). A maximum thiophene content of 2.5 mg litre (-1) was observed on the 13th day. Correlations were developed without taking the initial values of biomass, conductivity and osmolarity. Systematic experimentation was carried out in order to determine the relative significance of gas-liquid and solid-liquid mass transfer, which will form the basis for the selection of a suitable bioreactor for this system. At any given shaker speed the biomass growth (g litre (-1)) decreased with increasing volume of the culture medium. Similarly at any given volume of the culture medium biomass growth increased with an increase in shaker speed. The former indicates the importance of gas-liquid mass transfer, while the latter emphasizes the importance of solid-liquid mass transfer. The thiophene content also showed a similar trend with the variation of rotation speed and media volume. These results led to the inference that T. patula hairy roots are relatively non-shear sensitive. The observations of the present study provide guidelines for the selection of a suitable bioreactor for the cultivation of T. patula hairy root cultures.