Sixty patients who were scheduled to have an elective total hip or knee arthroplasty were randomly assigned to one of three groups of twenty patients each before operation with spinal anesthesia. A double-blind technique was used throughout the study. The patients in Group I (control group) received hyperbaric 1 per cent tetracaine with epinephrine as the subarachnoid spinal anesthetic; the patients in Group II (morphine group), hyperbaric 1 per cent tetracaine with epinephrine and a single subarachnoid dose of Duramorph (morphine sulphate), 0.5 milligram; and those in Group III (Dilaudid group), hyperbaric 1 per cent tetracaine with epinephrine and a single subarachnoid dose of Dilaudid (hydromorphone hydrochloride), 0.002 milligram per kilogram of body weight. During the first twenty-four hours after the operation, the patients in Group II and Group III had significantly less pain compared with those in Group I. This was shown by the use of a visual linear-analog pain scale (p less than 0.05), the patients' ratings of the quality of relief of pain (p less than 0.02), and comparative measurements of the pain-altering medications that were used (p less than 0.05). The patients in Group II and Group III did not have any more complications or side effects than those in Group I. There was no significant difference in the quality and duration of analgesia between Group II and Group III.