The system described here uses a hose-cable combination to tow a fishlike body containing a pump and a CSTD (conductive-salinity-temperature-depth) probe at depths of 135 m (or less) while the towing vessel is underway at speeds in excess of 5 m d ( 1 0 kn). This survey unit has the capability of pumping 6 L/min of seawater to analytical equipment on deck while simultaneously measuring the salinity, temperature, and depth at which the towed body is deployed. An on-deck data acquisition system automatically records physical, chemical, and biological data and provides real-time displays that can be used to modify the design of the survey as it is conducted. Optimum utilization of this system requires a heavy investment in analytical equipment and is therefore best accomplished by multidisciplinary programs. Such operation generates far more data than are normally obtained by oceanographic vessels and can substantially increase the efficiency of research ship utilization for studies of the “mixed” layer.