Experiments were made on the anisotropic growth mechanism of tabular grains, according to which the predominance of their lateral growth rate over the vertical was ascribed by Jagannathan et al. to rapid growth of the self-generating {100} faces on their side surfaces at low pBr. This mechanism was supported by analyses of the preferential adsorption of a dye to {100} faces on the side surfaces. The lateral and vertical growth rates of tabular silver bromide grains at critical supersaturation were measured in reaction solutions with varied pBr values as functions of their equivalent circular diameter (D_c) and thickness (h). The lateral growth rate at low pBr was larger than the growth rate of cubic grains and increased with increasing D_c and decreasing h, whereas the vertical growth rate at low pBr was smaller than the growth rate of octahedral grains. This result indicates that the diffusion of solute ions through the solution from the vicinity of the main surfaces to that of the side surfaces enhanced the anisotropic growth of the grains at low pBr. At high pBr, the lateral and vertical growth rates were small, nearly equal to each other, and decreased with increasing D_c, obeying the diffusion-controlled scheme. At some intermediate pBr, the lateral growth rate decreased with increasing D_c and was still much larger than the vertical growth rate, providing the opportunity for the precipitation of monodisperse tabular grains.