This study reports our first-year experience in the immunocytochemical staining of specimens prepared by the ThinPrep processor. The avidin-biotin-complex technique was applied to smears of 70 cytological specimens, including fine-needle aspiration samples from various sites (56 specimens), body fluids (13 specimens) and urine (one specimen). The specimens were collected in CytoLyt solution to lyse red blood cells and then resuspended in the processing solution. The smears were made by the processor and fixed in 95% alcohol. The panel of antibodies used included alpha-fetoprotein, carcinoembryonic antigen, cytokeratin, chromogranin A, HMB-45, beta-human chorionic gonadotropin (beta-HCG), Kappa, Lambda, Ki-1, leucocyte common antigen, L26, neuron-specific enolase, 013, prostatic acid phosphatase, prostatic-specific antigen, S100, thyroglobulin, UCHL-1, and vimentin. The various antigens could be easily demonstrated in the ThinPrep smears, except for some lymphoma markers. Nonspecific background staining caused by blood and proteinaceous debris was virtually absent. In general, the monolayer preparation made the interpretation easier than conventional preparations. The only problem with this technique was in the classification of lymphomas where immunotyping was inconclusive. Our preliminary results indicate that ThinPrep smears are suitable for immunocytochemical studies, except for the classification of lymphomas.