To evaluate hormone receptors immunohistochemically, standardized staining procedures and scoring systems are required. The authors previously reported that highly sensitive procedures affected basic factors for technical validation. The aim of the present study was to show the characteristics of scoring systems for highly sensitive procedures. To examine how highly sensitive procedures enhance the staining intensity and increase the positive cell population, two different staining methods were compared. To evaluate scoring systems, three systems--cell counting score, modified immunoreactive score, and H score--were compared using the same samples stained by an autostaining system. It was found that the highly sensitive procedure increased the positive cell population, especially in breast cancers with a low enzyme immunoassay (EIA) level of less than 100 fmol/mg, and strengthened the staining intensity. This enhancement led to a correlation in a logarithmic curve rather than a linear correlation by all three scoring systems. The results showed that scoring systems including a factor of staining intensity did not have an absolute advantage because boosted staining intensity by highly sensitive procedure did not reflect EIA value or protein contents accurately. To the authors' knowledge, there is no report discussing the nonlinear correlation between biochemical and immunohistochemical assay by highly sensitive procedures; however, it is important to select a scoring system and threshold based on nonlinear correlation.