AbstractA simplified model of the very early Universe is presented for studying the effects of the GUT phase transition on the cosmic evolution and vice versa. An exact description of a strongly first order phase transition is given. Both inflationary and non‐inflationray solutions are obtained. The cosmological scale factor and the temperature are determined and graphically depicted. The self‐consistency of our simplifying assumptions needed to get analytic solutions are checked. Contrary to expectations spread in the literature, the strongly first order character of the phase transition in itself is found to be insufficient to solve the monopol problem inherent in most GUT cosmologies.