The single laboratory test is used to establish the data quality that can be achieved within a single laboratory. It provides a basis for deciding whether or not a given method merits collaborative testing and it more clearly defines a method's potential for inclusion as part of an operational monitoring network. This summary provides a brief description of the suggested procedures for single laboratory testing. Phases of the single laboratory test include identification of procedural variables that must be carefully controlled (ruggedness testing), evaluation of method sensitivity, identification of the limits of reliable measurement, evaluation of systematic error (bias), and identification of method precision and accuracy. The chemical composition of all sample material must be verified during the single laboratory test. Sample material should have a concentration range, in the same sample matrix, that would be encountered if the method was being routinely used for its intended purpose. Some phases of the test should make use of certified reference materials.