The purpose of this study was to compare changes in pain threshold caused by meperidine, naproxen sodium, acetaminophen, and placebo. The change in pain threshold was measured by electric pulp testing. Acetaminophen elevated the pain threshold statistically significantly. Clinically, however, the superiority of acetaminophen is questionable. No elevation of the pain threshold occurred with narcotic drugs or with nonsteroidal anti-inflammatory drugs: our research shows that the electric pulp tests of patients who have taken these drugs preoperatively will have results similar to those of patients who have taken no drugs. We question the philosophy of administering these drugs for change in pain threshold at the levels used here preoperatively.