Abstract: A filter assembly comprising a filter retainer apparatus, an air filter frame and having a removable pleated filter media. The pleated filter element is secured within the frame by the retainer apparatus which comprises an expandible retainer having elongated flanges disposed on opposite ends. One flange is secured to a rod which slidably fits within a sleeve to which the other flange is attached. Resilient apparatus, preferably an elongated helical spring positioned between the sleeve and the rod, keeps the flanges in spaced relationship. One of the flanges engages one end fold in the filter element and forces it into contact with the frame. The rod is then forced into the sleeve compressing the spring and the other flange engages the other end fold of the filter element, forcing the other end fold into contact with the frame. The spring forces the rod and the sleeve apart so that the flanges securely hold the filter element in the frame.