The Tauber trap was subjected to tests in the controlled water flow of a flume to assess its sampling efficiency for a range of pollen types and varying speeds of flow. The equipment and procedures of pollen preparation are described, and the method of trap efficiency calculation is explained, Results indicating numerical differences in amounts of pollen caught by two sizes of trap are attributed to scaling factors on the traps used, and the increased flow velocity near the floor of the flume. Similar pollen proportions from these traps in each experiment are obtained, indicating an even distribution of pollen within the flow. Collection efficiency for individual taxa are found to vary both according to size and weight of the grains and the velocity of flow. Within one experiment, other factors being constant, smaller grains arc trapped less efficiently than those larger. The total experimental evidence suggests that, with increasing water speed, differences in grain characteristics have Jess effect, though the overall trapping efficiency is lowered. Factors of weight rather than density are proposed as determining the final catch from water by this particular design of trap. The significance of under- and over-representation of grains at low flow velocities is discussed in relation to the potential use of the trap as a pollen sampling mechanism in the field.