The cardiovascular effects of thiopentone 3 mg kg-1 and midazolam 0.3 mg kg-1 were observed during induction of anaesthesia in 16 premedicated patients about to undergo myocardial revascularization. There were no significant changes in either group in cardiac output or central venous pressure. The heart rate in both groups showed an increase at 3 min and thereafter returned to control values. After 3 min, there was a significant decrease in both arterial pressure and peripheral resistance by 12% and 15% (mean values) respectively from control values in the group receiving midazolam, whereas after thiopentone the peripheral resistance increased by approximately 13% and was not affected by a further dose of thiopentone 1 mg kg-1.