Mass transfer to the wall of a bubble column is examined, focusing on the influence of the liquid viscosity. The effect of introducing structured packing in the column is analysed by comparing results for the empty column with those of packed column at similar operating conditions. Visual observation allowed detecting of flow transition in the empty column with non-Newtonian fluids; hence, data obtained in a different flow regime are correlated separately. Results from the empty and packed columns could be correlated by the same expression. indicating that the presence of the structured packing inside the bubble column has no remarkable influence on the liquid to wall mass transfer. Expressions of the form St =f(Re, Fr, Sc) or Sh =f(Sc, Ga, E), mostly used in investigations on heat or mass transfer in bubble columns, are proposed. (c) 2005 Elsevier B.V. All rights reserved.