Abstract: An in-line agitating device for fluids includes an elongate internally-threaded cylindrical tube, open at each end, with a flow-disturber such as a round ball positioned inside the tube so as to substantially but not completely block off the bore of the tube. When a fluid is introduced into one end of the tube, its velocity increases as it is forced through the restricted space between the ball and the inner surface of the tube and then rapidly decelerates, causing turbulence which results in vigorous agitation of the fluid. This agitation is intensified by swirling action imparted to the fluid by the internal threading of the tube.