Pre-emptive intramuscular (i.m.) vasopressors were evaluated in 108 patients undergoing elective Caesarean section under spinal anaesthesia, assigned to four groups in a randomized, double-blind, placebo-controlled study. Group 1 received pre-emptive phenylephrine 4 mg i.m., group 2 received phenylephrine 2 mg i.m., group 3 received ephedrine 45 mg i.m., while controls received an i.m. injection of saline, all given immediately after induction of spinal anaesthesia. Hypotension was defined as a 25% decrease in mean arterial pressure (MAP). Rescue intravenous (i.v.) boluses of ephedrine were given if the patient was hypotensive or reported nausea, vomiting or dizziness. The incidence of hypotension was 33% in the phenylephrine 4 mg group compared with 70% in the control and phenylephrine 2 mg groups (P=0.03), and 48% in the ephedrine 45 mg group. The phenylephrine 4 mg and ephedrine 45 mg groups had a significantly lower percentage reduction in MAP (-21 (SD 14)% and -22 (14)%) compared with controls (-32 (18)%, P=0.04). They also had a lower total dose of rescue i.v. ephedrine (15.7 (15.7) mg and 15.8 (15.6) mg) compared with controls (28.8 (20.6) mg, P=0.02). We conclude that pre-emptive i.m. phenylephrine 4 mg and ephedrine 45 mg reduce the severity of hypotension and the total dose of rescue i.v. ephedrine during spinal anaesthesia for Caesarean section.