We have measured the electrical resistance and magnetoresistance near the metal-insulator transition in films of the amorphous alloys Gd x Si 1 - x and Y x Si 1 - x (x~0.14-0.15) for 0.1K<T<20K in an applied magnetic field 0kOe<H<105kOe. In a low magnetic field, a-Gd x Si 1 - x is an insulator and the conductivity approximately follows the expected behavior for variable range hopping. With increasing field H the conductivity of a-Gd x Si 1 - x increases by ~3 orders of magnitude at low T, crosses through an insulator to metal transition and approaches the conductivity of a-Y x Si 1 - x indicating that the effect of the magnetic Gd impurities on transport is dimished by the application of a magnetic field. The low-temperature conductivity on the metallic side of the transition scales approximately linearly with the applied magnetic field, indicating that the critical exponent μ~1.