The crystallization of proteins is a topic of great interest since the availability of macroscopically large crystals represents almost the only means available to characterize native protein structures by scattering techniques. Two decades of experiments have shown an extremely simple phenomenology describes this crystallization process: proteins crystallize if their second virial coefficients fall in a very small band [“crystallization slot”]. Since such universal behavior has been observed it appears reasonable that simple models, such as spheres interacting through isotopic interactions, are sufficient to understand these situations. We have employed a series of computer simulations to study the validity of this simple model in describing protein crystallization: the results of this investigation will be discussed in this talk