An ultrasonic inspection apparatus is disclosed for inspecting coextruded plastic sheet as it is produced. The apparatus includes support for the sheet to be inspected and support for an ultrasonic transducer adjacent the surface of said sheet. A housing supports the ultrasonic transducer adjacent the sheet and defines a chamber between the face of the transducer and the surface of the sheet. The chamber is provided with an interfacing fluid so that ultrasonic pulses from the transducer will pass through the fluid into the sheet to be reflected from any interface therein. The ultrasonic transducer and interfacing fluid are moved across the surface of the sheet to permit inspection of the entire sheet. Means are provided within the fluid chamber for directing interfacing fluid substantially transversely across the face of the transducer to remove any air bubbles that may form between the transducer face and the sheet. The ultrasonic pulse echoes received from the sheet may be analyzed to provide an indication of the presence and depth of interfaces in the sheet.