The aim of this study was to establish if the cholecystokinin (CCK) 2 antagonist L-365,260 augments the analgesic effect of morphine in human subjects with chronic neuropathic pain. This is a randomised, double blind, placebo controlled study of 40 adult subjects taking morphine for neuropathic pain. Each received placebo, L-365,260 30 mg and L-365,260 120 mg in three divided doses daily separated by a washout period in random order. Pain, activity, sedation, sleep and side effects were recorded along with 12 lead ECGs, renal and liver function tests and full blood pictures. L-365,260 failed to augment the analgesic effect of morphine at any of the dose levels used. Side effects were minor. There were no changes in ECGs and biochemical indices were unaltered with its use. The CCK 2 antagonist L-365,260 does not augment the analgesic effect of morphine in subjects with chronic neuropathic pain. L-365,260 was well tolerated and side effects from its use were minor.