The origin of functional differences between motoneurons of varying size was investigated by employing a one-compartmental motoneuron model containing a slow K+ conductance dependent on the intracellular calcium concentration. The size of the cell was included as an explicit parameter. Simulations show that motoneurons of varying size cannot be regarded as simple 'scaled' versions of each other. Rather, they are expected to have intrinsic properties that vary with cell size. These intrinsic properties refer to the membrane conductances per unit area and the dynamics of the intracellular calcium concentration.