The quality of the liquid flow distribution is investigated at the outlet of a 30-cm-diameter trickle bed by means of a liquid collector divided in nine compartments and inside the bed by local heat transfer probes. Coalescent and coalescence-inhibiting fluids are employed. In steady-state operation, the liquid flow maldistribution, quantified using the collector, attains a minimal value for a superficial liquid velocity of about 0.006 m s(-1). At lower superficial liquid velocities, the important maldistribution is due to the stochastic nature of the trickling liquid flow, whereas at higher superficial liquid velocities, the increase of the maldistribution is due to the formation of a radial flow gradient, characteristic for the pulsing flow regime. Measurements of the local particle-liquid heat transfer coefficient indicate an important spread of the local particle irrigation, probably due to geometrical reasons. The influence of periodic operation of the liquid feed rate is tested. Under the investigated operating conditions, periodic operation is not found to improve significantly the liquid distribution at the two spatial scales investigated: the maldistribution quantified by the collector measurements and the spread of the local particle-liquid heat transfer coefficient are almost invariable. (C) 2004 Elsevier B.V. All rights reserved.