Abstract: A nanovolume microcapillary crystallization system allows nanoliter-volume screening of crystallization conditions in a crystal card that allows crystals to either be removed for traditional cryoprotection or in situ X-ray diffraction studies on protein crystals that grow within. The system integrates formulation of crystallization cocktails with preparation of the crystallization experiments. The system allows the researcher to select either gradient screening in crystallization experiments for efficient exploration of crystallization phase space or a combination of sparse matrix with gradient screening to execute one comprehensive hybrid crystallization trial.