The Avidin and Biotin solutions are color-coded with a
pH indicator. In most cases, endogenous biotin in tissue sections is masked by
formalin fixation. However, if avidin-biotin IHC detection systems are used with
frozen sections or tissues pretreated with a heat-induced, epitope retrieval
method (HIER), an avidin-biotin blocking technique may be needed. It can also be
used on an automated staining system.