An environmentally controlled case is described for conserving a Fayum panel painting on loan to the Brooklyn Museum which exhibited a high degree of sensitivity to changes in relative humidity. The case was constructed of aluminum with a glass front, sealed in an air-tight fashion with a gasketted metal frame. It was intended to maintain a level of 50% RH in order to relax the panel painting from its high degree of warping, returning it to its original contour, and to conserve it permanently in this microclimate. The humidity control agent used for this purpose was silica gel. The authors have detailed the construction of the case and method of installation of the Fayum portrait, as well as the technique of silica gel maintenance.