A system for monitoring, recording and storing arterial pressure and heart rate during continuous extradural analgesia has been developed using an Apple II microcomputer and a Dinamap 1846 non-invasive arterial pressure monitor. The administration of local anaesthetic (or vasopressor) was recorded using a light pen. The computer was programmed to recognize this, and to initiate automatically more frequent measurements of heart rate and arterial pressure. The results of a study using this equipment are reported. The commands for computer control of the Dinamap 1846 are described.