The results of this paper suggest that a modified translog function (MTL) is a suitable functional form to model milk production. Marginal products estimated from the MTL. model are, in general, quite similar to their Cobb- Douglas (C-D) counterparts. However, the substitution elasticity parameters obtained from the two models are markedly different. Returns to size measures derived from the MTL and C-D models are almost identical and reveal slightly increasing returns to scale.