The recommended optimal concentration of adjuvant epinephrine for use with local infiltration anesthesia is usually 5 µg/mL. However, a lower dose might be as effective at prolonging the anesthetic effects, while limiting the risk of hazards associated with unintentional intravascular injection. The aim of our study was to determine the lowest effective vasoconstrictor concentration of epinephrine in human skin for a range of doses of bupivacaine and its less-vasodilatory S(-) isomer, levobupivacaine. We injected combinations of 0.125%, 0.25%, and 0.75% bupivacaine and levobupivacaine with 1.25, 2.5, and 5 µg/mL epinephrine into the forearm skin of 10 healthy volunteers and measured the resulting blood flow changes over 1 hour using laser Doppler imaging. All 3 concentrations of epinephrine produced marked vasoconstriction, both alone and in combination with all 3 doses of the anesthetics (P < .001 in all cases). There was almost no difference in effect between the 3 epinephrine concentrations. We conclude that 1.25 µg/mL epinephrine produces a comparable vasoconstrictor effect in human skin to that of higher concentrations when coinjected with clinical doses of bupivacaine and levobupivacaine and may be equally effective for infiltration anesthesia.