Relative intensity fluctuations in single-mode class B lasers, i.e., a laser diode (LD) and a microchip Nd YVO(4) solid-state laser (SSL), were examined. Experimental observations revealed significant difference in the characteristics of the LD and the SSL. A stochastic laser model and the Fokker-Planck equation approach were used, and reduced moment equations were developed. A close agreement was achieved between the theoretical and experimental results. As indicated by the theoretical analysis, the intrinsic parameter of the lasers; i.e., the time ratio between the lifetimes of the carrier density (population inversion) and the photons, is crucial to fluctuation dynamics.