Sorption isotherms and scanning data were obtained for three test materials at three different temperatures. These data resulted from further investigating the operating range of an existing experimental apparatus and procedure. During the course of the research, the operating range and control of the existing apparatus were extended, and its temperature range was tested for the first time. The apparatus is composed of a small test chamber, which is capable of containing from one to six test samples, and an external forced-air relative humidity and temperature conditioning system. The conditioning system maintains test chamber relative humidity and temperature, as directed by a GW-BASIC computer program. Sample moisture content is gravimetrically determined in situ. The system can maintain dry-bulb temperatures between 10 C and 70 C. At room temperature, the apparatus can maintain relative humidities between o and 90 per cent. Low temperature set points have a significantly lower maximum relative humidity range as a result of the formation of condensation in the concentric tube counterflow heat exchanger. High temperature set points are also severely limited, due to the formation of condensation in the test chamber during data collection. Sorption isotherms were measured for oriented strand board, fiber board sheathing, and exterior grade plywood over the relative humidity range limits at 12 C, 25 C, and 55 C. Scanning curves were measured from the 50 per cent relative humidity set points on the adsorption and desorption curves of the 25 C isotherms. / Master of Science