A series of 1378 intra-operative frozen diagnoses performed in our department over two years (1998-1999) was studied in order to assess the agreement with the diagnosis on formalin-fixed, paraffin-embedded sections. In selected cases, a rapid immunostaining (IS) method was applied on frozen sections to solve diagnostic problems. Rapid IS allowed us to determine the histotype of poorly differentiated neoplasms, the origin of lung nodules and the presence of nests of neoplastic cells on resection margins. The method delayed the answer by about 20 minutes, and was always previously arranged with the surgeon. Rapid IS method was performed using routine reagents and was not repeated on formalin-fixed, paraffin-embedded sections of the same cases, thus avoiding additional costs.