Immunocytochemical staining of cultured cells using specific antibodies is a powerful technique to study the expression and subcellular localization of proteins. However, this technique is associated with sample-to-sample variations because samples are handled individually and manually. Cell permeation is needed when intracytoplasmic or nuclear proteins are studied. Storage of cultured cells is difficult, and experiments must be repeated if additional studies are desired later, which introduces more variations. We developed a cell culture block array technique that converts cultured cells into a permanently fixed form identical to tissue sections prepared for pathologic examination. Cells from different cultures can be embedded in a single block. Many identical sections, each containing cells from multiple cultures, may be stained with different antibodies using an automated stainer. As a result, sample-to-sample variation is eliminated. Because cells in these blocks are sectioned by knives, all cellular proteins come into direct contact with antibodies, and cell permeation is not needed. Such blocks can be conveniently stored for years without loss of antigens, providing a constant source for future studies. We demonstrated the utility of this technique by studying the proliferation and neuroendocrine differentiation of prostate cancer-derived LNCaP cells cultured in vitro.