A dilute solution parameter obtained from static light-scattering measurements is proposed as a predictor for protein crystallization experiments. The osmotic second virial coefficients, B(22), have been measured for a variety of proteins in solvents that are known to promote crystallization and the values for B(22) were found to lie within a fairly narrow range which we refer to as a crystallization slot. Solution conditions which were known not to favor crystallization of the proteins resulted in B(22) values well outside the crystallization slot.