This paper describes the design of a modified gas sampling probe for measuring gas temperatures and humidities in a two-phase flow, based on the layout of Kieviet et al., [EG. Kieviet, J. Van Raaij, P.J.A.M. Kerkhof, A device for measuring temperature and humidity in a spray drying chamber, Trans. Inst. Chem. Engrs, Part A, 75 (1997) 329-333]. This device separates small particles from the gas how by means of the difference in inertia between the fluid and the particles. Two mechanisms of separation are employed successively, namely a swirling motion and a sharp change in direction of the flow. A small fraction of the clean flow is then directed to a thermocouple and subsequently to a dew-point hygrometer. The commercial computational fluid dynamics (CFD) package CFX4.2 has been used to assess the performance of the probe and to optimise the flow rates of the main and the clean air flow. Experimental testing confirms the prediction that this probe is able to measure temperatures and humidities in two-phase flows accurately down to particle diameters of 5 mu m in droplet-laden flows. Due to deposition of wet solids on the swirl vanes, the separation performance for them decreases, so that only wet particles of more than 16 mu m can be separated. (C) 2000 Elsevier Science S.A. All rights reserved.