Baryogenesis in models with a low quantum gravity scale

We make generic remarks about baryogenesis in models where the scale M-s of quantum gravity is much below the Planck scale. These correspond to M-theory vacua with a large volume for the internal space. Baryogenesis is a challenge, particularly for M(s)less than or similar to 10(5) GeV, because there is an upper bound on the reheating temperature of the Universe, and because certain baryon number violating operators must be suppressed. We discuss these constraints for different values of M-s, and illustrate with a toy model the possibility of using horizontal family symmetries to circumvent them. [S0556-2821(99)06410-3].