Hypertension following coronary surgery is generally reported at an alarmingly high incidence (30 to 75 per cent). A vigilance program carried out in 1977 at the Montreal Heart Institute disclosed a low incidence of 3.5 per cent in 200 consecutive unselected cases. A similar program in 1980 based on 160 cases showed an incidence of 23.7 per cent. This highly significant difference is found to be related to the differences in anaesthetic management which have occurred since 1977 when anaesthesia was primarily morphine 1.0 to 1.5 mg . kg-1 supplemented as needed with low dose halogenated agents and vasodilation therapy. In 1980, only one of the authors (J.T.) still uses this technique. The incidence of hypertension in 40 of his patients was 2.5 per cent. The others use low dose fentanyl (7.5 to 10 micrograms . kg-1) supplemented as needed with halogenated agents and vasodilating therapy; the incidence of hypertension in 160 cases was 23.7 per cent. Would these results be the same with an anaesthetic technique comparing both drugs at equipotent doses? A prospective clinical study is addressing this question.