Using a radioisotopic tracing technique, new data on back-mixing and mass transfer parameters have been obtained from the residence time distribution (RTD) of the liquid in an air-water cocurrent downflow trickle-bed reactor containing six different types of porous particles. Data reduction of the measured liquid RTD has been carried out using the comprehensive axial-dispersion-exchange + intra-particle diffusion RTD model of Iliuta et al. (Chem. Eng. Sci. 54 (1999) 4099) which accounts for liquid back-mixing in the dynamic zone, the intra-particle diffusion, and the mass transfer effects (i) between the dynamic zone and nearby partially wetted particles, (ii) between the stagnant zone and adjacent partially wetted particles, (iii) across the dynamic-static boundary. The effect of gas and liquid feed flow rates on the liquid axial dispersion coefficients, the liquid-liquid mass transfer coefficients between stagnant and dynamic liquid zones, and the liquid-solid mass transfer coefficients between static liquid and subtended wetted fractional pellet areas was investigated.