The c-axis resistivity p, in BizSrzCaCuz08+b and oxygen-reduced YBazCu306+" is quite sensitive to a magnetic field H. The magnetoresistance (MR) is large (1% at 14 T and 100 K), weakly anisotropic, and negative over a wide range of temperatures T above the critical temperature T, . The magnitude of the MR is activated in temperature with a characteristic energy Uz that varies with the oxygen content 8. We interpret the activated form of p, and the negative MR in terms of a pseudogap 5 that is slightly reduced by H.A distinctive property of the cuprate superconductors is their anisotropic electrical resistivity at temperatures T above the superconducting critical temperature T, . In the underdoped regime, the c-axis resistivity p, displays an insulating trend (increases at T decreases) while the in-plane resistivity p, b is "metallic" in behavior.

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