Immunohistochemistry is no longer a technique used only for research but is employed increasingly for diagnosis and for the assessment of therapeutic biomarkers. The latter, in particular, often require a semiquantitative evaluation of the extent of their presence. There are many factors that can affect this that relate to the method: fixation of tissue, duration and type of antigen retrieval, antibody specificity, antibody dilution and detection systems. Other complexities relate to assessment. Different scoring systems are used for either the same or different antigens. Cut-off levels for assessing whether a tissue is 'positive' or 'negative' can vary for the same antigen. Whilst there are quality assurance schemes for the methodology that have improved standards of staining, there are no similar schemes that relate to interpretation, although errors here can create as many problems. There have been improvements in automated analysis but availability is limited and it is still predominantly a research tool. In order for quantification of immunohistochemistry to be a reliable and reputable tool, there must be easy to use, reproducible, standardized protocols for assessment which are international. Improvements in automated analysis with wider applicability could lead to standardization.