In contrast to the standard nucleation theory, in which thermodynamic (macroscopic) variables are used, the present theory uses atomic (microscopic) variables. This leads to a system of stochastic equations. For the case of extremely high supersaturations, the single atom represents the critical nucleus. Condensation is then not an activated but merely a pure deposition process. This described by a simplified set of equations (IIa). Its solution shows that during the early phase of film formation the adatom concentration changes with time as follows: (1) linear growth, (2) constant, and (3) t − 1 3 decrease. Furthermore, the adatom concentration never exceeds a certain maximum value for a given condensation rate. For this reason the nuclei density as observed in a electron microscope becomes independent of temperature below a certain substrate temperature. If this effect exists it should make possible the determination of the two basic parameters τ A and w.