In cooperatation of the Institute of Hydromechanics and Water Resources Management with the Institute of Geodesy and Photogrammetry at ETH Zurich a fully automatic 3-D Particle Tracking Velocimetry System based on digital multimedia photogrammetry has been developed, which offers high spatial resolution, accuracy and reliability. The paper will first describe the hardware components of a digital photogrammetric PTV-system, which mainly consists of off-the-shelf products. The major parts of this hardware are the ilumination system consisting of a strobelight or a laser plus beam shaping optics, the imaging system with three or more synchronized CCD cameras and videorecorders for intermediate data storage, and a PC equipped for digitization of long video image sequences. To be able to follow structures in a channel flow for a longer time period both the imaging and illumination system can travel together with the average velocity of the flow. The chain of data processing contains an exact calibration of the system, digital image processing, a strict mathematical modelling of the complex geometry given by three cameras in arbitrary orientation in combination with the broken beams due to different refractive indices, and a flexible tracking algorithm for following particles in time through 3-D space. Special emphasis will be put on the reliable solution of ambiguities proved to be crucial when working with high particle densities in the flow; it also showed that a reliable determination of 3-D coordinates is only possible with at least three cameras imaging the flow. In applications of the method a maximum of more than 1000 instantaneous velocity vectors could be determined, and an accuracy of better than 0.1 mm for all three displacement vector components in a test volume of 250 X 250 X 40 mm was obtained. Results will be presented from experiments on an open channel flow, in an agitated tank and from the determination of the flow field in a buoyant puff. (A)