Pain management after total hip replacement is one of the most important aspects of postoperative care for patients and clinicians alike. One of the most common techniques used in anesthesia for this procedure is spinal anesthesia with concurrent administration of opioids into spinal sac. Addition of opioids not only prolongs the anesthesia but also provides pain relief after the procedure for a limited amount of time. Because of its unique chemical properties morphine provides the longest pain relief amongst currently known opioids lasting up to 24 hours. Unfortunately this beneficial effect is associated with both minor and serious adverse effects, most important of which is respiratory depression. To limit this potenitialy fatal adverse effect dosing of morphine must be very precise in order to balance advantages and risks. The aim of the study was to assess effectiveness and safety profile of different doses of morphine administered during spinal anesthesia for pain control.