Abstract: This invention relates generally to crystal growth devices, and more particularly to a device in which protein crystals are grown in a hanging drop (12). The drop (12) is suspended from a surface (32) positioned in the interior (21) of an enclosure (18) which is sealably coupled via a valve (56) to a vessel (16) containing solvent used in the drop (12). A second opening in the enclosure (18) is coupled via a valve (54) to a vessel (14) containing a selected desiccant material (44). The valve (56) may be fully or partially opened to add a selected quantity of solvent in a vapor phase to the drop (12), and the valve (54) may be fully or partially opened to cause a selected quantity of solvent to evaporate from the drop (12). The process is monitored by a camera (70), and in conjunction with a graduated pattern superimposed over the drop (12), relative volumes of the drop (12) are determinated.