The use of antigen retrieval techniques has been the foundation of the development of immunocytochemistry (ICC). After the pioneering work done on cryostat sections, the use of enzyme digestion made formalin-fixed archival and current material available for study by ICC. However, the relationship between the duration of fixation and the digestion time necessary for optimum results is a major drawback associated with enzyme digestion. The longer the tissue has been in fixative, the longer the required digestion time will be. Even after a standardised fixation time, some antigens require greatly extended digestion times. Whereas 10-15 minutes in trypsin may be a standard protocol after overnight fixation, immunoglobulin deposits in renal glomeruli may require 60-90 minutes.