Marine turbidity currents provide an explanation, frequently the best or only explanation, for a wide variety of phenomena. The circumstantial evidence for their efficacy is very convincing, but there is scant empirical evidence bearing on their mode of origin and none on the presence of high-density, high-velocity currents in the ocean. Experiments intended to simulate the conditions of nature have been conducted on the sea floor off San Diego, California, in an attempt to produce high-density currents. The experiments were conducted by sliding a mass of pre-mixed sediment from an elevated, tilted container 40 ft. below sea-level on a naturally sloping sea floor and observing the resulting flow directly by utilizing SCUBA. The initiation of a flow appears sensitive to the proportions of the sediment grain sizes and therefore cohesiveness of the sediment mass, the method of mixing, and total volume. Initiation on an open slope appears much less likely than on the walls of a confined feature such as a gully or canyon. Natural analogies do not tend to support the existence of high-density high-velocity, marine turbidity currents.