This chapter deals with relatively simple ways to use control charts to monitor the performance of ELISAs. A rinderpest competition ELISA, for the estimation of antibodies in serum samples, is used to demonstrate the methods. This assay is available in kit form. Constant evaluation of the use of the kit is part of what is called internal quality control (IQC). Figure 1 shows an overview of the ELISA scheme described in this chapter. The details of the procedure, which involves plotting the data graphically (charting methods), are explained herein. The objectives of charting data are as follows:

1.	To keep a constant record of all data.
2.	To monitor the assay from plate to plate in any one day’s testing.
3.	To monitor the tests made from day to day, week to week, year to year.
4.	To allow rapid identification of unacceptable results.
5.	To allow recognition of reagent problems.
6.	To identify trends in results (increasingly poor performance).
7.	To identify when a new set of kit reagents is necessary.
8.	To allow identification of differences in operators of the assay.
9.	To fulfill various criteria for good laboratory practice.
10.	To fulfill necessary requirements for external recognition that tests are being performed at an acceptable level (increasingly important when results are used for international trading purposes).