The effect of dental injection of local anesthetic on arterial plasma epinephrine concentrations and cardiovascular functions was assessed in patients having a maxillary third molar extracted. After three and five minutes, arterial plasma epinephrine concentrations were more than two times higher than baseline values in patients who were given an injection of a standard Carpule (1.8 ml) of 2% lidocaine with 1/100,000 epinephrine (18 micrograms). The heart rate and pressure-rate product increased slightly above baseline control values, and the mean arterial pressure declined slightly (P less than .05) after five minutes. Patients who received an injection of lidocaine alone had no significant change of plasma epinephrine or of the cardiovascular parameters measured. Although the hemodynamic responses to lidocaine plus epinephrine in these healthy young adults were small, the significant increase of systemic plasma epinephrine concentrations suggests that high-risk patients who receive this type of anesthesia should be monitored carefully.