The absorption rates of NO in a CrO3/H2SO4/H2O solution have been investigated. A gas/liquid stirring cell and a pilot packing column were used. The experiments, which covered a wide range of gas and liquid concentration, are discussed using the film theory of gas absorption accompanied by a fast chemical reaction. The reaction was found to be second order in NO and first order in CrO3. The rate of NO absorption increases if either the H2SO4 or CrO3 concentration or the NO partial pressure is increased. Good agreement between experimental data and theory is only obtained when the concentration terms in the model are replaced by activities. In a further step, a scale-up from stirring-cell experiments to a pilot packed column was performed. A high surplus of reactants (500 gl(-1) H2SO4 and 50-150 gl(-1) CrO3), which is common in technical applications, led to a simple expression for the mass transfer term. (C) 1997 Elsevier Science B.V.