In an apparatus and method for agitating a sample during dissolution or other in vitro testing, a movable component is disposed in a container for reciprocating or rotating a sample carrier such as a dosage form or stent through a medium in the container. The apparatus can include a closure member to seal the container for substantially preventing loss of contents during movement of the sample carrier. The movable component can be actuated by a driving source in a non-contacting manner. The movable component can include a magnet drivable by a source external to the container. The container can include first and second container sections having different volumes, in which case actuation of the movable component causes agitation of the sample carrier through a medium contained in one of the container sections. The container can include a hole at or near the bottom for filling the container, using instruments, and the like.