In a recent work (Gibilaro et al., 2006) a general expression for the apparent viscosity of a solid-fluid suspension was derived by making use of the concept of particle bulk mobility: a general relationship for the dependency of apparent suspension viscosity on particle volume concentration was found without the use of any fitting parameters; in the case of dilute suspensions the result is practically coincident with the relationship proposed by Einstein, derived theoretically for neutrally buoyant suspensions. In this work, experimental support is extended to non-neutrally buoyant systems, i.e. systems where the density of the suspended solid differs considerably from that of the fluid. The suspension apparent viscosity has been estimated from the measured settling velocity of a single test sphere falling through dilute solid-fluid suspensions in the viscous flow regime at various particle concentrations (up to 0.05). Measured values are in excellent agreement with predicted values. Moreover, test particle settling velocities were found to be linearly dependent on the suspension particle concentration, as predicted by Batchelor (1982). It is also shown that, on the basis of the pseudo-fluid approach, the apparent viscosity of the suspension derived from Batchelor's expression for the settling velocity is coincident with the Einstein relationship.