Objectives: To evaluate the prophylactic effect of norepinephrine (NE) and vasopressin (VP) infusion on frequency and severity of spinal anaesthesia-induced hypotension (SAIH). Patients and methods: A total of 240 young male patients were randomly allocated into three equal groups: Group C received plain saline infusion, Group NE received NE infusion (0.1 mg/ml; 3 ml/h) and Group VP received VP infusion (0 5 U/ml; 1 U/h); all infusions started synchronously with spinal injection (SI). Systolic arterial pressure (SAP) and heart rate (HR) measures were determined at 1, 4, 7 and 10-min; then every 5-min for 30 min. SAP reduction of >10% was treated by supplementary fluid therapy and resistant cases or patients who had SAP reduction of ≥20% received ephedrine (10 mg). Results: In comparison with baseline SAP, SAP was decreased by > 20% in eight control patients, by 10%, while 15 patients had increased SAP of > 10% and 145 patients showed no SAP change with significant difference between the two groups (p = 0.0003). Throughout the 30 min after spinal block, all SAP and HR measures of control patients were significantly (p = 0.001) lower compared with their baseline measures and with corresponding measures of patients of the NE and VP groups with non-significant difference between the two groups. Seven patients (8.8%) in the control group had nausea and three (3.8%) had nausea and vomiting, while no patient in the NE and VP groups had nausea or required anti-emetic therapy. Conclusion: Vasopressor infusion given synchronously with spinal injection is an appropriate prophylactic policy against SAIH. NE infusion did better than VP infusion and provided better haemodynamic stability after spinal injection. However, VP infusion allowed control of blood pressure despite the significant decrease till 7 min after SI.