We have measured the magnetoresistance curves of a silver‐clad Bi (2223) tape below critical temperatureTcover a magnetic field range up to 8 T. At temperatures well belowTcthe magnetoresistive transition can be well described by a thermally activated flux flow (TAFF) process. The activation energies inferred from such dissipation measurements are found to have the formU=U0+U’(H,T), whereU0is magnetic field and temperature independent,U’(H,T) is proportional to (1−T/Tc)n/H. At temperatures very close toTcthe TAFF dissipation can no longer be found and the magnetoresistance seems to be determined by the combination of viscous flux flow and thermal fluctuation. ©1995 American Institute of Physics.