A preliminary study was conducted to determine the feasibility of developing an on-line x-ray diffraction (XRD) monitor to determine gypsum during wall board manufacturing. Samples of bassanite (CaSO4 . 1/2H(2)O) containing 0, 1, 3, and 5% gypsum (CaSO4 . 2H(2)O) were analyzed in the laboratory using an experimental on-line XRD monitor and a conventional x-ray diffractometer. Results of this study indicate that the development of a gypsum monitor is technically feasible. When sample packing was used, gypsum was detected in all of the samples containing added gypsum and the sensitivity was adequate to differentiate between each of the gypsum concentrations. Without sample packing, 1% gypsum could not be detected under the analytical conditions employed. The precision was reasonably good for these exploratory tests, with relative standard deviations ranging from 10-30%. Precision can probably be improved through instrument modifications. Once developed an on-line gypsum monitor is anticipated to cost on the order of $75,000.