The performance of an Elag-Koln semiautomatic blood pressure recorder was compared with the London School of Hygiene mercury sphygmomanometer in 24 subjects providing a wide range of blood pressure measurements. Readings with the two instruments correlated highly (for systole, r=0-99; for diastole phase 4, r=0-97; for diastole phase 5,r=0-98), and the slopes of the regressions did not differ significantly from unity. Elag-Koln measurements were higher for systole (mean difference 3-7 mmHg,P less than 0-001) and diastole phase 5 (mean difference 7-4 mmHg,P less than 0-001), but agreed closely with diastole phase 4 readings with the London School of Hygiene instrument. The Elag-Koln recorder tested was compact, easy to use, and had acceptable accuracy. This type of instrument deserves further testing to examine its suitability for general use.