A moored self-recording instrument designed to measure the fine scale temperature and velocity vector variability of the ocean in a vertical plane containing the mean velocity vector is described. (Since the conception, design, and naming of the microscale sensing array (MSA) the scale designation of phenomenon with wave lengths in the range (0) 1 to (0) 10 m has been changed from 'microscale' to 'fine scale.') The structure holds 16 water velocity sensors (propellors) and 14 water temperature sensors (thermistors). These sensors are mounted along two vertical masts, each 8 m long, separated horizontally by a 20-m spar. The whole structure is rigid, buoyed by two aluminum spheres, each 1 m in diameter, providing a net buoyancy for the instrument of about 386 kg. Contained within the spheres are an electronic data acquisition system, a magnetic tape recorder, primary batteries, a compass, and accelerometers to measure roll and pitch attitude. A separate cylindrical housing contains a pressure transducer and preamplifiers to sense depth. Provision is made to measure MSA translational motion by means of an acoustic transceiver and remote transponders. Instrument life is primarily dependent upon tape storage (53 million bits) and data sampling rate, which is easily preset to various continuous or burst modes. Maximum allowable operating depth is presently 900 m. The MSA has been deployed four times in the main thermocline southeast of Bermuda and once in the New England Continental Shelf bottom boundary layer.