An ultrasonic apparatus for producing particles of a pharmaceutical agent or other material comprises a flow-through ultrasonic horn comprising an inlet, an outlet, and an interior channel that connects the inlet to the outlet for flow of a fluid therethrough. The ultrasonic horn is connectable to a transducer, and a crystallization tube is adjacent to the ultrasonic horn. The crystallization tube comprises an inlet port and outlet port for flow of an antisolvent therethrough, and it further includes a side access port. The outlet of the ultrasonic horn is inserted into the side access port so as to be in fluid communication with the crystallization tube.
