Accurate modeling of load behavior inZ‐pinch plasma radiation sources driven by high‐current generators requires the measurement of fast‐rise‐time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B‐dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by highdI/dt. In this paper, we describe the use of large‐signal, nanosecond‐time‐resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressureB2/2&mgr;0=&mgr;0I2/8&pgr;2r2generated at radiusrby a currentIflowing in a radial transmission line. Current measurements have been performed at radiusr=2.54×10−2m on Sandia National Laboratories’ Proto‐II (10 TW) and SATURN (30 TW) gas puffZ‐pinch experiments with maximum currents of 10.1 MA anddI/dtto 2.1×1014A/s. Comparisons with Faraday rotation and B‐dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y‐cut lithium niobate stress gauge on a pure tungsten electrode, current densities up toI/2&pgr;r=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X‐cut quartz piezoelectric element and a tungsten‐sapphire electrode impedance stack.