A new conductivity probe technique is applied to high-speed, pulsed diesel sprays to measure the dimensions and time dependency of the breakup zone. Variations are made of liquid properties, gas density, and orifice size. A flat-plate probe is used to detect the contiguous liquid in the breakup zone. Breakup length is of the order 100 nozzle diameters at engine conditions of gas density, and a increases with increase of liquid viscosity and reduction of gas density. Typically, of the order of 1% of injected liquid is measured to be incompletely atomized at 100 diameters downstream. Some agreement with published correlations for breakup length is found; however, a is shown that liquid viscosity should be included in correlations and analyses of breakup, and not simply the ratio of liquid and gas density as in some previous work. A revised correlation gives reasonable agreement with the new data. The breakup length is found to vary throughout the spray pulse, reflecting, in a complex manner, the time-varying flow rate produced by a conventional injector and pump. Periodicity of the breakup zone structure is noted at frequencies of the order 10 kHz, and this appears to be in accordance with published results using photography and laser anemometry.