Aim of the present study was to investigate the efficacy of 4 different proteolytic treatments (Ficin, Protease type XIV, Microwave irradiation in Citrate buffer and Microwave irradiation in Lead Tiocyanate), compared to the incubation with buffer only, for the detection of cytokeratins in 10 cases of carcinomas from different organs. The same anti-cytokeratin antibody was applied to two sets of tissue sections, after proteolytic treatment, and the reaction was developed by using a different method (ABC or APAAP) for each set of slides. The semiquantitative evaluation of the specimens demonstrated that the higher number of immunoreactive tumor cells was present after Microwave irradiation in Lead Tiocyanate and, to quite a lesser extent, in Citrate buffer. Ficin and Protease type XIV appeared less effective and in some circumstances, the enzymatic digestion of tumor cells seemed to negatively affect the quality of immunostain. When buffer only was used the percentage of immunoreactive tumor cells was considered to be unreliable for diagnostic purposes. The results of the study seem to suggest that proteolytic pretreatment is essential to avoid false negative results when cytokeratin immunostain is essential in histopathology and that Microwave irradiation in Citrate buffer is eligible as the best procedure.