Acoustic Doppler current profilers, ADCPs, arrived on the oceanographic scene a decade ago as a development of ship‐mounted Doppler speed logs to measure vertical profiles of horizontal water velocities. Backscattered acoustic intensity is one of the parameters that can be recorded and early anecdotal observations indicated that intensity variations had distinctly biological characteristics such as diel zooplankton migrations. These early observations led to an ongoing study of the conditions under which ADCPs might be able to make quantitative estimates of zooplankton biomass. The attraction of ADCPs, and the motivation for the study, is not so much the ADCPs' ability to discern details about zooplankton populations but rather their ease of use and general availability. The results of the study to date, with operating frequencies of 150 and 300 kHz, have shown that ADCPs produce biomass estimates to within ± 15% throughout their acoustic range when the individual transducers have been calibrated and proper care is exercised in processing the results. ADCPs provide the ability to conduct nonintrusive large‐scale surveys, in either time or space, of zooplankton biomass providing input, for example, to ecological models and as guides to more conventional sampling schemes.