The onset of pulse flow in trickle-bed reactors involving gas-non-Newtonian liquid systems was predicted from a stability analysis of the solutions around equilibrium steady-state trickle flow of a transient two-fluid model based on the volume-average mass and momentum balance equations. The model was developed for the versatile Herschel-Bulkley constitutive theological equation from which special solutions for plastic Bingham fluids, power-law shear-thinning and thickening fluids, as well as Newtonian fluids were derived. The impact of yield stress, consistency and power-law indices, and temperature and reactor pressure on the trickle-to-pulse flow transition was analyzed theoretically. Model predictions of the trickle-to-pulse transition for gas-non-Newtonian liquid systems were confronted with elevated temperature and pressure experimental transition data obtained for air-0.25 and 0.5 mass(carboxymethylcellulose) CMC solution systems measured by means of an electrical conductivity technique. In addition the model version offspring corresponding to the Newton case (n = 1, k =mu(l), tau(0) = 0), confronted with measured high temperature/pressure-transition data from this work and high-pressure transition data from Wammes et al. [1990. The transition between trickle flow and pulse flow in a cocurrent gas-liquid trickle-bed reactor at elevated pressure. Chemical Engineering Science 45, 3149; 1991. Hydrodynamics in a cocurrent gas-liquid trickle bed at elevated pressures. A.I.Ch.E. J. 37, 1849] and Burghardt et al. [2002. Hydrodynamics of a tree-phase fixed-bed reactor operating in the pulsing flow regime at an elevated pressure. Chemical Engineering Science 57, 4855] proved equally successful. (c) 2005 Elsevier Ltd. All rights reserved.