Diacetyl for blocking the histochemical reaction for arginine

Two different histochemical methods for blocking the guanidinium group of arginine in formalin fixed, paraffin embedded material are reported here. One procedure uses diacetyl with short incubation times and high pH, the other uses the trimer of the diacetyl reagent and requires longer incubation times but moderate pH. The diacetyl reagent is recommended despite its high pH because the preparation of the diacetyl trimer is laborious and time-consuming.