RW models with variable G and constant active gravitational mass

We find that the incorporation of the conservation of active gravitational mass in Einstein's theory demands the variation of G or Lambda for baryonic matter. If G is allowed to vary, keeping Lambda constant, this demands Lam bda less than or equal to 0. For Lambda < 0, the model uniquely determines the curvature parameter k = -1 with a sinusoidal expansion. An interesting case arises when Lambda = 0. In this case, G is a decreasing function of ti me in the early universe and becomes constant as the universe turns matter dominated reducing the models to the standard FRW models in the present pha se of evolution.