A dissolution test cell for use with a continuous flow dissolution test apparatus and method wherein a dosage form is contacted with media and the media is analyzed for concentration of an active substance, said dissolution test cell comprising: a vessel having a chamber for holding the media and dosage form therein, at least one inlet and at least one outlet, each of said at least one inlet and at least one outlet being in fluid communication with said chamber for passage of media and dissolved materials; a tight-fitting lid attached to said vessel for enclosing said chamber and preventing uncontrolled fluid communication between said chamber and the ambient environment, said lid comprising: an opening for passage therethrough of a dosage form into said chamber; and a slide valve assembly sealingly affixed to said lid proximate said opening and having: (a) a planar member which is moveable between an open position, in which fluids and materials are permitted to pass through said opening and into said chamber, and a closed position, in which fluids and materials are prevented from passing through said opening; (b) an actuator in communication with said planar member and being externally accessible for moving said planar member between its open and closed positions during operation of said dissolution test cell; a dosage form holder having a compartment and which is removably and sealingly attached to said slide valve assembly wherein, when said planar member of said slide valve assembly is in its open position, the compartment is in fluid communication with said opening and said chamber, whereby a dosage form is permitted to pass from said compartment, through said opening of said lid, and into said r chamber; and a mixing device for mixing the media, dosage form and dissolved materials in said chamber. a vessel having a chamber for holding the media and dosage form therein, at least one inlet and at least one outlet, each of said at least one inlet and at least one outlet being in fluid communication with said chamber for passage of media and dissolved materials; a tight-fitting lid attached to said vessel for enclosing said chamber and preventing uncontrolled fluid communication between said chamber and the ambient environment, said lid comprising: an opening for passage therethrough of a dosage form into said chamber; and a slide valve assembly sealingly affixed to said lid proximate said opening and having: (a) a planar member which is moveable between an open position, in which fluids and materials are permitted to pass through said opening and into said chamber, and a closed position, in which fluids and materials are prevented from passing through said opening; (b) an actuator in communication with said planar member and being externally accessible for moving said planar member between its open and closed positions during operation of said dissolution test cell; an opening for passage therethrough of a dosage form into said chamber; and a slide valve assembly sealingly affixed to said lid proximate said opening and having: (a) a planar member which is moveable between an open position, in which fluids and materials are permitted to pass through said opening and into said chamber, and a closed position, in which fluids and materials are prevented from passing through said opening; (b) an actuator in communication with said planar member and being externally accessible for moving said planar member between its open and closed positions during operation of said dissolution test cell; (a) a planar member which is moveable between an open position, in which fluids and materials are permitted to pass through said opening and into said chamber, and a closed position, in which fluids and materials are prevented from passing through said opening; (b) an actuator in communication with said planar member and being externally accessible for moving said planar member between its open and closed positions during operation of said dissolution test cell; a dosage form holder having a compartment and which is removably and sealingly attached to said slide valve assembly a mixing device for mixing the media, dosage form and dissolved materials in said chamber.