Breakthrough pain in patients with cancer is common, often unpredictable, and can rapidly become severe. Treatment using the oral administration of opioids is not optimal due to the slow onset of pain relief. Nasal administration of analgesics potentially offers more rapid pain relief. This study investigates the tolerability and efficacy of a novel morphine-chitosan formulation. Twenty episodes of breakthrough pain were observed in 14 patients with cancer who received 5-80 mg of nasal morphine-chitosan. Nasal symptoms, sedation, giddiness, nausea, and other volunteered symptoms, along with pain scores (pain intensity and pain relief), were recorded at baseline and at regular intervals up to 4 hours after administration, together with an overall satisfaction rating. The formulation was acceptable to patients, generally well tolerated, and had an onset of pain relief 5 minutes after dosing. This formulation warrants further study.