OBJECTIVE: To investigate infusion pumps start-up delay according to different brands of infusion pumps, flow rates and intravenous sets priming techniques. METHOD: The experimental study simulated clinical practice under controlled conditions, using a 50 mL syringe with NaCl 0.9% solution, two syringe infusion pumps (A and B), six rates (0.3, 0.5, 1.0, 5, 10 and 20 mL/h), two purging techniques (manually or infusion pump's electronic bolus). Data were analyzed according to mean, standard deviation, Student's t and ANOVA tests (p<0.05). RESULTS: The start-up delay was greater in low rates regardless the priming technique. The electronic bolus increased the infusion pump A accuracy at 0.3mL/h (p=0.010), 0.5 mL/h (p=0.002) and 1.0mL/h (p=0.004). Pump's accuracy in all studied rates and manual IV sets filling was similar. CONCLUSION: In low infusion rates the start-up delay was greater despite the infusion pump brand and electronic bolus improved pumps accuracy.