Initialization of a separably stiff system of ordinary differential equations consists of readjusting certain initial values, while holding the others fixed, in such a way that the solution of the system does not have an initial transient. This paper discusses the features of a FORTRAN program which solves the initialization problem. The algorithm used is simpler and faster than those used previously. Numerical results are given for a simple test problem and more complex problems which arise in the physics of the upper ionosphere and the solar wind.