It is presented a method useful to form ordinary differential equations from nonlinear regression models of the type , a power series allowing to directly retrieving the differential model from raw data after fitting, to be differential equation itself. compared with the differential model expected for the biological system which is studied. In particular for any possible value of n, the highest power at which the independent variable is raised, the paper gives the method to get the differential equation having the polynomial as solution. The use of power series allows some practical advantages when dealing with differential equations, and one of these - in some