 Colorectal surgery is a frequent operation with expected strong post-operative pain. Thoracic epidural analgesia is a preferred method by many authors, but it is not without risks. As patients in our hospital usually stay at a surgical ICU for 24 hours only and epidural infusion of opioids is prohibited at standard wards according to our hospital standards, it seems to be too demanding method. Systemic analgesia with strong opioids is usually an alternative, but high doses of opioids are known to cause side effects. The last possibility is a single-shot intrathecal injection of morphine which demonstrated long-lasting analgesia after various procedures. The main advantage is easy technique, absence of catheters and low cost. There are not enough studies to decide which method is the most convenient. The purpose of this prospective randomized open clinical study is to determine which postoperative analgesia is optimal after colorectal surgery. The investigators will compare intrathecal morphine, continuous epidural analgesia and compare both methods to standard systemic analgesia. All patients will have the possibility to administer themselves intravenous morphine as needed. 