A simple, inexpensive mechanical device is described for the direct continuous measurement of mean arterial pressure. It can be assembled in minutes using a few dollars worth of sterile components commonly available in an intensive care unit. Mean arterial pressure determined in patients with this device differs by 1.6 mmHg .+-. 1.1. SD from mean arterial pressure simultaneously measured by properly calibrated Hewlett-Packard electronic monitors (N = 5), a non-significant difference. Similar agreement was obtained when the device was tested using a commercial blood pressure system calibrator as the pressure source. This device also allows rapid static calibration of electronic pressure transducers across the full range of human blood pressure using a 3 ml syringe as the pressure source and an aneroid gauge, or mercury column, as the pressure standard.