Abstract: An apparatus and method determines the dissolution of a drug from a dosage form, most particularly a swellable dosage form. An inert, transparent cylindrical vessel having a hemispherical bottom contains a fluid medium. The dosage form is placed into the vessel. A disk carried in the vessel has a pair of annular rings for engaging the vessel walls spaced above the bottom of the vessel. The disk has a screen mesh circumferentially sandwiched by the rings for passage of the fluid medium through the disk. A dosage form retaining space defined between the disk and bottom of the vessel retains the dosage form. The disk restrains the dosage form from floating to the top of the fluid medium. A stirring mechanism having a vertical shaft and a blade at a lower end of the shaft is inserted into the vessel. The stirring mechanism rotates the fluid medium. The drug concentration in the fluid medium is sampled at selected time intervals.