I have some frozen sections, which were imbedded in OCT. I tried to stain them with HE, using standard protocols, but failed. Is it caused by the OCT? How to get rid of the OCT (It seems that xylene does not work)? Or I have to use paraffin to imbed the sample?

OCT is very water soluble, so you could try a quick water rinse before hematoxylin, then rinse with water until clear and begin your dehydration up until eosin.

what tissue are you trying to stain?