We report the data of direct and indirect immunofluorescence labelling of peripheral blood mononuclear cells obtained from 40 normal controls and nine patients having blood tests for non-haematological disorders (PNHD controls) using flow cytometric analysis. Polyclonal and monoclonal antibodies were used to define the expression of cell surface antigen of T cells, their subsets, B cells, natural killer cells (NK) and myeloid cells. Normal values of absolute number and percentages of each of the populations of mononuclear cells were established and were sufficiently reproducible to be of clinical use. The percentages of positive values of T cells, T-cell subsets, and B cells in ten normal controls when mononuclear cells were used, were comparable to those using whole blood lysis, APAAP immuno-alkaline phosphatase, and E and M rosettes. The results obtained were similar in both the normal and PNHD controls. In most instances the percentage recovery of identified T, B and NK cells was complete. Currently we are using the results as reference values for lymphoid sub-populations in normal controls.