Immunoassay methods often have higher CVs than observed for routine chemistry and hematology tests. Laboratory QC practices often involve analyzing 3 or 4 different levels of controls and sometimes analyzing these controls in duplicate. In planning QC for such applications, it is useful to assess the error detection and false rejections characteristics of higher N multirule QC procedures and see how they compare with the performance from more common QC procedures having Ns of 2 to 4.