Measurements of transport alternating‐current (ac) losses in Bi2Sr2CaCu2O8+xpowder‐in‐tube Ag‐sheathed tapes at 4.2 and 65 K and at 20, 60, 200, and 400 Hz were carried out and comparisons to the theoretically predicted hysteretic loss plus ohmic loss were made. The measured loss, albeit larger than predicted, was found to agree with Bean’s critical state model. The loss, having a linear dependence on the frequency of the alternating transport current and increasing with decreasing critical current density, confirms hysteresis as the dominant source of power dissipation at both 4.2 and 65 K. However, at 4.2 K, the loss varies as the square of the amplitude of the transport current, which is not consistent with the model. ©1995 American Institute of Physics.