Quality assurance in laboratory medicine includes: a) constant checking of test reliability by internal quality control (IQC), b) external quality assessment (EQA) by an independent agency to check performance of a number of laboratories at intervals in order to obtain a retrospective indication of their performance, and c) proficiency control by supervision of pre-test and post-test phases of laboratory work, from specimen collection to delivery of report to the clinician. In the UK the majority of laboratories are aware of the importance of IQC and to a greater or lesser extent they all perform some IQC procedures. These are briefly described, with special reference to the special requirements of haematology. A description is also given of the organizational structure of the EQA scheme which was established in the UK at a national level (UK NEQAS). This has an important role in ensuring good laboratory practice in both the national health service and the private sector.