Effectiveness of hydraulic jet agitation systems of agrochemical sprayers was investigated by measuring the concentration of a kaolin clay/water mixture in the line to the boom. Experiments were conducted on several sprayer tanks of different capacities and agitator types. An initial series of tests identified the most important parameters affecting the efficiency of a particular agitation system. An experimental design was chosen to determine the effect of each parameter as well as interactions among them. An agitation index was used to evaluate the effectiveness of each agitation system separately, regardless of tank size and shape. Statistical analysis of agitation effectiveness (AGEF) values showed that the system pressure was the most important factor affecting agitation effectiveness through its direct influence on jet velocity. If the jet velocity was kept constant, then the volume of fluid delivered into the tank was the most important factor in enhancing mixture uniformity. (C) 2000 Silsoe Research Institute.