Abstract
A simple model of globular proteins which incorporates anisotropic attractions is proposed. It is closely related to models used to model simple hydrogen-bonding molecules such as water. Theories for both the fluid and solid phases are presented, and phase diagrams calculated. The model protein exhibits a fluid-fluid transition which is metastable with respect to the fluid-solid transition for most values of the model parameters. This is behaviour often observed for globular proteins. The model offers an explanation of the difficulty observed in crystallising some globular proteins and suggests that some proteins may not have a solid phase at all under all but extreme conditions.