A simple analytical model is applied to study the effects of macromolecular crowding on the stability of partially folded states of the murine prion protein. It is found that relatively low levels of macromolecular crowding stabilize the partially folded states. The magnitude of the stabilization effect is similar for the partially folded to that of the fully folded state. Thus, the model suggests that it is on pathway molten globule-like states, rather than partially folded states arising from unfolding of the native state, that play a key role in the pathogenic interconversion mechanism under crowded conditions.