The biochemical assay for the oestrogen receptor has shown the clinical val
ue of knowing the concentration of the receptor within tissue. The immunohi
stochemical assay is rapidly taking over from the biochemical assay. Theref
ore, it is vital to have an equivalent scoring system that will have the sa
me predictive value. This paper reports both a practical protocol and a sco
ring system that should achieve this aim. This approach should be applicabl
e to many more biomarkers detected by immunohistochemistry.