A comparison of the Bull's algorithm (XB) for quality control with a system based on analysis of preserved blood suggested that the preserved blood approach was the more sensitive method. However, the procedures compared were not equivalent. Four control blood samples analyzed by a multirule Shewhart approach were compared with a single XB result. Consequently, a reexamination of the relative sensitivities of the two methods was undertaken with a multirule Shewhart approach applied to both methods. On this basis, both methods have equivalent sensitivity. Once the XB mean reflects the shifted mean (and at all times with a drifting mean), either the XB algorithm or the analysis of preserved blood will detect systematic errors with similar probability using similar control rules.