Abstract: A system and method for determining macromolecule crystallization conditions by measuring the polarization anisotropy of a fluorescent probe attached to the macromolecule in solution as a function of a variation in crystallization conditions. In one exemplary embodiment, the concentration of the macromolecule material is varied and the polarization anisotropy as a function of concentration gives an indication of the proximity to crystallization conditions. A pulse illumination system with time gated detection is disclosed to isolate fluorescence response from excitation to reduce noise due to scattered and reflected light. A microassay system is disclosed to allow a complete 96 condition screen with less than 1 micro-liter of solution.