Most experimentation dealing with analytical methodology in the physical and biological sciences has been conducted within a single laboratory. Method validation by other laboratories was considered not only unnecessary but also detrimental because, in the words of one commentator, 'the results are too variable'. Within the last two decades, however, largely as a result of the requirements of international environmental and food standards programmes, it has become increasingly apparent that a collaborative interlaboratory study is the only way to estimate the variability characteristics of methods of analysis as performed by the typical population of laboratories using the methods. To obtain a common basis for measuring the statistical characteristics of analytical methods, representatives of almost two dozen international organizations meeting in Geneva, in May 1987, approved by consensus a protocol for the design and interpretation of data from collaborative studies of chemical methods of analysis.