This article provides a description of a diagnostic developed to allow spatial and temporal measurements of the average vertical liquid mass flux within a pulsing spray. The diagnostic incorporates a patternator similar to that used in spray research for measuring mass distributions within sprays. For this application, the patternator section consists of a row of sample tubes oriented normal and intersecting the injector axis. However, in addition to the patternator section, the diagnostic incorporates a rotating shutter mechanism, which allows phased or transient sampling of the mass within transient spray plumes. To date, the technique has been successfully applied to a number of pulsing injection systems to produce spatially resolved measurements of transient mass flux. To illustrate the capabilities of this diagnostic, sample mass flux data are provided for a pulsed fuel injector. In this case, mass flux was a strong function of time and space, and measurements were possible for all regions of the spray, independent of spray number density or liquid void fraction. ©1997 American Institute of Physics.