Tramadol hydrochloride is a synthetic opiate agonist with a plasma elimination half-life of 5 to 6 hours and peak plasma levels at about 1 1/2 hours. It derives its activity from attachment to the mu-receptor and blockage of norepinephrine reuptake. The purpose of this single-dose, double-blind, placebo-controlled study was to determine the analgesic effectiveness of an oral administration of two dose levels of tramadol hydrochloride (75 or 150 mg) compared with the combination of 650 mg acetaminophen plus 100 mg propoxyphene napsylate in 161 patients with severe postoperative pain after cesarean section. Analgesia was assessed over a 6-hour period. Treatments were compared on the basis of standard scales for pain intensity and relief and a number of derived variables based on these data. A global rating of the study medication was also used to compare treatments. The three active treatments were effective analgesics, statistically superior to placebo for many hourly and summary measures. A dose response was seen between the two tramadol doses, with the 150 mg dose providing significantly greater analgesia over the lower dose. The 75 mg dose of tramadol was generally more effective than the acetaminophen-propoxyphene combination after hour 2, and significantly so for some hourly time points, as well as for the global rating of the medication. The 150 mg dose of tramadol was significantly more effective than the acetaminophen-propoxyphene combination from hour 2 through hour 6 for the sum of pain intensity differences and total pain relief scores, as well as for the global rating of the medication. Tramadol hydrochloride at both dose levels is an effective analgesic agent and at 150 mg is statistically superior to the acetaminophen-propoxyphene combination. No serious adverse effects were observed; however, dizziness was more frequently reported with 150 mg tramadol.