OBJECTIVE: To examine the feasibility of the use of a cell block preparation of Epstein-Barr virus (EBV)-infected Burkitt's lymphoma cell line (EB-3) as a positive control for in situ hybridization (ISH) for EBV-encoded RNA (EBER). STUDY DESIGN: EB-3 cells were processed into cell block and cytocentrifuge preparations. ISH for EBER was performed, and the results were compared with a commercially available EBV positive control slide (cytocentrifuge). RESULTS: The cost of preparing the cell block and cytocentrifuge sample was only a fraction of the price of commercial control slides. ISH for EBER was strongly stained in all preparations with similar intensity of staining but with a much higher number of positive cells in the cell block. Although the cellular details in the cell block were considerably inferior to those on the cytocentrifuge and commercial control slide, with distortion of nuclei and smudging of chromatin, the interpretation of the ISH results was unaffected. The cell block was stable at room temperature when examined after one year. CONCLUSION: The cell block preparation of an EBV- infected Burkitt's lymphoma cell line serves as a reliable, stable and a relatively inexpensive control, with good preservation of cellular details of cellular RNA for ISCH study for EBER in the detection of latent infection with EBV.