The development of sensitive reagents and detection systems, together with the introduction of heat-induced antigen retrieval, has rapidly entrenched immunohistology as an indispensable adjunct to routine histological examination, contributing to diagnosis, prognosis and treatment. New antibodies continue to be produced and new applications for "old" antibodies are described. The production of antibodies enabling the detection of genetic abnormalities, including mutations, gene amplifications and specific chromosomal translocations associated with novel chimeric proteins, promises to yield further insights into the genesis and behaviour of tumours. The ability to stain for target molecules that regulate tumour growth and proliferation is essential for selecting tumours for treatment with monoclonal antibodies. The mechanism of antigen retrieval remains debated. The absence of optimal controls continues to hinder standardisation of immunostaining and invalidates current attempts at quantification of immunostaining.