Objective. The objective of this study was to determine the anesthetic efficacy of the intraosseous injection as a primary technique in human maxillary and mandibular teeth. Study design. Forty subjects received two sets of intraosseous injections with 1.8 ml of 2% lidocaine with 1:100,000 epinephrine at two successive appointments. The experimental teeth consisted of 40 groups of maxillary and mandibular first molars and lateral incisors. Each experimental tooth and adjacent teeth were tested with an electric pulp tester at 4-minute cycles for 60 minutes. Anesthetic success was defined as no subject response to the maximum output of the pulp tester (80 reading) for two consecutive readings. Results. Anesthetic success occurred in 75% of mandibular first molars, in 93% of maxillary first molars, in 78% of mandibular lateral incisors, and in 90% of maxillary lateral incisors. Overall, for the intraosseous injection onset was immediate, the duration of pulpal anesthesia steadily declined over the 60 minutes, there was a 78% incidence of subjective increase in heart rate, the majority of the subjects had no pain or mild pain with perforation and solution deposition, and 3% of the subjects had slow healing perforation sites. Conclusions. The results of this study indicate that the intraosseous injection may provide pulpal anesthesia in 75% to 93% of noninflamed teeth as a primary technique. However, the duration of pulpal anesthesia declines steadily over an hour. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;81:634-41)