Morphine sulfate, a narcotic analgesic, possesses the undesirable side effects of central depression, tolerance, and dependency. Opiate receptors have been found in the brain and the spinal cord. Intrathecally applied opiates produce potent analgesia that can be antagonized by naloxone. The time-response study with tail-flick response after intrathecal injections of a small dosage of morphine (25 μg) demonstrated a long-lasting analgesia. Intrathecal injections of morphine or opiate-like peptides may become a predictable modality of pain relief without attendant loss of other neurologic function.