The role of the androgen receptor in the regulation of prostate cancer development and progression has been a focus of intense research. Until recent years, the level of expression of the androgen receptor protein was described qualitatively. Immunohistochemical parameters have been established that show a linear relationship between androgen receptor expression and immunostaining. Intensity of immunostaining can be accurately measured using computer-assisted color video image analysis. Studies of progression and treatment of prostate cancer will benefit from the ability to quantitatively measure androgen receptor expression.