We investigate the behavior of isotropic models in the general scalar-tensor theory of gravitation. We derive the criterion for inflation to occur in a range of such theories, including that of Brans and Dicke. The solutions used to model "extended" inflation in earlier investigations are shown to be special cases which do not follow the behaviour of the general Brans-Dicke model at early times. The conformal relationship between scalar-tensor theories and general relativity with a self-interacting scalar field is explored and used to find members of a new class of inflationary universes. These "intermediate" inflationary universes have expansion scale factors which increase as exp(tp), 0 < p < 1. The possibility of successfully of realizing the ◀old" inflationary universe scenario in these models, with the present time variation of the gravitation "constant" being acceptably small, is illustrated with a specific example.
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