An unexpected phenomenon emerges from the model equations governing single-mode homogeneously broadened lasers. Conditions have been identified analytically under which the laser output can be made to switch from low to high (or high to low) intensity through a small variation in the parameters of the medium, for example, the pump rate. The results are distinct from those involving transitions at a 'second laser threshold' to regions of bistability, multistability and chaos. The transition described here arises from the inclusion in the analysis of fluctuating forces in the medium. A similar scheme can be used to describe a familiar transition in physics-the Curie-Weiss ferromagnetic transition.