Flow cytometric detection of intracellular antigens has become a standard method in establishing proper leukemic cell lineage affiliation. It has a non-debatable contribution to the diagnosis of hematolymphoid neoplasm as well as in minimal residual disease. Combination of analysis of fluorescence labeling and light scatter properties of cells allows rapid and better determination of target cell antigens. Regarding the detection of intracellular antigens, standardization of the procedure remains, however, a real challenge. Detection of intracellular antigens by flow cytometry (FCM) requires effective fixation and permeabilization of the cell membrane. In the available literature, some reports describe methodologies to achieve satisfactory results for detection of either cytoplasmic or nuclear antigens; however, no methodological consensus has yet been achieved among the laboratories. This article is an attempt to describe different approaches to detect intracellular molecules by FCM.