Backreactions in Superinflationary Cosmologies

We examine Jordan-Brans-Dicke theories with a linear potential for the scalar field by means of a stochastic approach. The backreaction of the scalar field fluctuations on the classical background is described. The analysis is concentrated on those values of the Jordan-Brans-Dicke parameter which predict a superinflationary pre-big-bang branch. The graceful exit problem present in these theories is discussed.