Quality assurance programmes are an efficient way of maintaining the standards of performance of diagnostic laboratories throughout the world, and of upgrading these standards where necessary. The quality of a laboratory test is generally considered to be synonymous with its reliability (accuracy) and its reproducibility (precision). However, in microbiology, quality goes beyond technical perfection to take into account the speed, the cost, and the usefulness or clinical relevance of the test. Laboratory tests in general are expensive and, with progress in medicine, they tend to use up an increasing proportion of the health budget.