The Colin ABPM 630 is a silent, gas-powered (CO2) ambulatory blood pressure monitor which uses both ausculatory and/or oscillometric methods to measure blood pressure. We compared simultaneous, same-arm blood pressures obtained with the monitor with those made by two blinded, skilled clinicians using a mercury column and teaching stethoscope. In a second study, the monitor readings were also compared with opposite-arm intra-arterial recordings of blood pressure. The group mean systolic blood pressures obtained by the Colin monitor via the Korotkoff mode were almost identical to the mercury column readings (127.8 +/- 19.4 versus 128.1 +/- 19.3 mmHg, P = NS) and the limit of agreement (2 standard deviations) for the differences in the two methods was +/- 9 mmHg. The diastolic blood pressure obtained by the Colin monitor was significantly lower than the clinician's readings (-6.0 +/- 5.9 mmHg, P less than 0.0001). Similar findings were obtained with the oscillometric mode, however, the mean systolic blood pressure given by the monitor was slightly higher than that given by the mercury column (1.9 +/- 4.5 mmHg, P less than 0.001). In contrast to the mercury column comparisons, the mean diastolic blood pressure obtained with the monitor was nearly the same as the mean intra-arterial diastolic blood pressure for both the Korotkoff (0.1 +/- 5.6 mmHg) and the oscillometric modes (1.2 +/- 6.3 mmHg). During 100-watt bicycle exercise, there was a considerably greater scatter in the individual comparisons of the monitor and intra-arterial blood pressure than that seen in the measurements at rest, but the group means were again similar.(ABSTRACT TRUNCATED AT 250 WORDS)