We analyze the behaviour of the Nusselt number in turbulent Rayleigh-Benard
convection of binary mixtures. We show that a power-law-type term dependin
g on an extended Rayleigh number is present in the expression of the Nussel
t number. In particular, for dilute mixtures, this is tie only contribution
to the Nusselt number and, just as: in the case of single fluids, a power
law is valid for the system.