The major historical developments in clinical measurement and also in statistics and computing are surveyed, and an outline of the problems to be considered in the thesis is given. Before dealing with clinical measuring processes in general, some methods for handling measurements are examined. In particular, procedures for dealing with replicate measurements are investigated. The evaluation of a single clinical measuring process is discussed with special reference to continuous auto-analysers such as the Coulter Cell Counter Model S. The main facets of evaluation of a single clinical measuring device are presented. Designs and the corresponding analyses are given for the simultaneous estimation of the accuracy, precision and carryover in the presence of drift. In some situations, linearity is also investigated. The results of some practical experiments are presented. To complete the discussion of the evaluation of measuring processes, the comparison of different clinical measuring processes for the same parameter(s) is investigated. A number of different methods of analysis are examined. Using clinical data, the results obtained from these analyses are presented. In a survey of quality control the basic requirements for control in the clinical field relevant to haematology, and in the haematological laboratory, are discussed. Quality control is seen to have two components - Intra and Inter laboratory control. An examination of both types of control is presented. These incorporate discussions of methods and procedures of control and related topics. An example of an intra-laboratory scheme, currently in use, is presented. In the discussion of inter-laboratory control, the results of a survey of the participants of the Department of Health and Social Security and British Committee for Standardisation in Haematology. Haematology Quality Control-Trials are presented. Finally conclusions, further areas for investigation and areas of development are presented and outlined.