A multiphasic linear model is presented that describes the allometric relation between body components and permits a smooth transition from one linear segment to the next. Three applications of a diphasic linear model to allometric growth problems were used to illustrate the model. The data sets were selected because a breakpoint exists in the allometric relation. Relations between growth of the alimentary tract and of empty body weight in rabbits, growth of length and of body weight in larval-carp and growth of protein and of fat in pullets were described by a diphasic allometric model. For rabbits and larval-carp, relations were described significantly better by a diphasic instead of a monophasic (simple) allometric model. For situations where response is expected to consist of more than one linear segment, the multiphasic model is recommended.