Aim of this study was to evaluate the blood pressure (BP) measurement reliability of a light weight ambulatory BP and ECG recorder. Micro AM is a new 300 g portable apparatus that combines in one device both the ambulatory BP and solid state ECG recording. The dimensions of the Micro AM are 75 x 140 x 29 mm. The monitor measures BP using Korotkoff phase 1 for systolic and phase 5 for diastolic BP, and concurrently measures oscillometric BP, one method validating the other. In addition, the manual and programmed BP measurement modes can be supplemented by an "intelligent" mode in which the ECG triggers an ambulatory BP reading during an abnormal ST segment change. A standard mercury manometer was connected with the cuff of the Micro AM with a Y-shaped part, and 12 BP measurements were simultaneously taken at 5 min intervals by the automatic device in auscultatory mode and by a trained technician in 86 normotensive volunteers (aged from 18 to 44 years, 37 males and 49 females). The algebraic differences, the frequency distribution and the difference distribution of systolic and diastolic data between the 2 methods were calculated. The results show that the automatic method gives values for systolic BP that are lower than conventional ones (average differences -0.643 mmHg), whereas for diastolic BP, the values are higher (average differences +0.229 mmHg). Then, Student's paired t-test was used to evaluate statistically significant differences. The test relative to systolic BP was significant to the critical level of 0.1%, but the differences being 3 times smaller than the instrumental tolerance. On the contrary, diastolic BP differences were non significant. In conclusion, we found a good agreement between BP recorded automatically and by sphygmomanometer.