Pain is a complex phenomenon involving both neurophysiological and psychological components. Pathophysiological mechanisms involve neural pathways, and a variety of pain-producing substances and modulating mechanisms. These include acetylcholine, serotonin, histamine, bradykinin, prostaglandins, substance P, somatostatin, cholecystokinin, vasoactive intestinal polypeptide, noradrenaline and endogenous opioid peptides. In assessing patients with pain, it is essential to evaluate the cause of the pain, its severity, type, location, duration, quality, and response to therapies, among other factors. The measurement of pain is dependent on subjective responses, which are evaluated by methods which have been well developed over the last three decades. Alleviation of pain by non-drug treatments must be considered as well as use of pharmacological treatments. These include psychological support, placebos, relaxation training, biofeedback, hypnosis, heat, cold, physical supports and surgery. Oral drugs are generally preferable to parenteral drugs, as are drugs with few side effects and low addictive liability. Both overtreatment and undertreatment are to be avoided. Patients can be expected to differ in their needs and responses, and economic considerations ought not be ignored. Newer approaches to pain management include self-administration of parenteral drugs, the search for new types of analgesics and appreciation of the relationship between age, sex, race, etc. and the response to analgesics. Tricyclic antidepressants, phenothiazines and the new non-steroidal anti-inflammatory drugs have pointed the way to possible improvements in our ability to tailor specific drugs to the needs of individual patients.