In this paper we study the isotropisation of a Generalized Scalar-Tensor
theory with a massive scalar field. We find it depends on a condition on the
Brans-Dicke coupling function and the potential and show that asymptotically
the metric functions always tend toward a power or exponential law of the
proper time. These results generalise and unify these of De Sitter in the case
of a cosmological constant and of Cooley and Kitada in the case of an
exponential potential.Comment: 10 page