An interlaboratory quality control scheme has been established in Britain by the British Committee for Standards in Haematology. In the first instance this has been confined to haemoglobin, red blood cell count, and packed cell volume. The materials which have been circulated include whole blood, stabilized red cell preparations, lysates, cyanmethaemoglobin solutions, and cyanmethaemoglobin reference preparations. The first two trials have been completed, and there are implications for instrument calibration, dilution techniques, and the use of standards. Periodic interlaboratory trials, at a national level, in conjunction with regular individual intralaboratory quality control procedures, are necessary in order to achieve acceptable levels of accuracy and precision.