In pseudoplastic aqueous solutions of polysaccharides (xanthan, hydroxypropyl guar), hydrodynamics and oxygen mass transfer were studied in bubble columns of 0.19 m, 0.29 m and 0.60 m diameter (0.08 to 1.6 m(3) liquid volume). Churn-turbulent flow prevailed; a slight diameter effect on the gas hold-up was observed only at high viscosity in the smaller columns. The volumetric mass transfer coefficients were independent of the column diameter. The suitability of previously suggested correlations for scale-up is analyzed.