This paper reports some recent experimental observations of both gas and gas-solid two-phase flows through small monolith channels. For gas flows, the laminar-to-turbulent transition in monolith channels was observed to occur at a Reynolds number of similar to 620, much lower than the conventional transition criterion of 2200 for large pipes. Surface roughness of and non-uniform distribution of gas in monolith channels were proposed to be possible reasons. For gas-solid two-phase flows, both pressure drop and solids hold-up were measured. It was found that the pressure drop of gas-solid two-phase flows through monolith channels was significantly lower than that through packed particle beds with even lower surface area per unit bed volume. Reprocessing of the pressure drop data in terms of the dimensionless groups showed that the Euler number depended approximately linearly on the solids-to-gas mass flux ratio for a given superficial gas velocity, and suspended particle size imposed little effect under the conditions of this study. Measurements of the solids hold-up showed that the hold-up in monolith channels increased with a decrease in both the gas velocity and the suspended particle size. The pressure drop results were also compared with semi-theories developed for pneumatic conveying. An overprediction was observed, an indication of the need for more controlled experiments for fundamental understanding of the hydrodynamics in monolith channels. The work reported here on gas solid two-phase flows through monolith channels represents the first attempt in this area as no previously studies have been found in the literature. (c) 2005 Elsevier B.V. All rights reserved.