Delivering the most effective clinical therapy in acute promyelocytic leukaemia (APL) is dependent on accurately making the diagnosis. The morphological diagnosis can be improved by detecting the presence of a specific chromosome translocation, the t(15;17)(q22;q21). This can be achieved using cytogenetics, RT-PCR, FISH and anti-PML monoclonal antibody. The optimal approach will be rapid, accurate and readily integrated into the routine haematology laboratory. Immunofluorescent detection of microparticulate PML protein fulfils these criteria, however, karyotyping will also detect the variant translocations and remains the 'gold-standard'.