Supersymmetry and Rb in the light of LEP 1.5

We re-examine the possible magnitude of the supersymmetric contribution to Rb ≡ Γ(Z0 → bb)Γ(Z0 → all) in the light of the constraints imposed by the absence of light charginos at LEP 1.5, implementing also other available phenomenological constraints. We find the supersymmetric contribution to be Rbsusy < 0.0017, and discuss the extent to which this upper bound could be strengthened by future constraints on the chargino and top-squark masses. Such values of Rbsusy tend to disfavor a supersymmetry explanation of the apparent Rb discrepancy.