Caerulein (CRL) (5 micrograms i.m.) and morphine (10 mg i.m.) have been tested for their analgesic activity in a double blind randomized study in a total of 36 patients with medium to severe tumor pains. A decrease of more than 20 mm on a visual analogue scale (VAS) was taken as a criterion for successful therapy. This was the case in 67% of the patients treated with morphine and 50% of those treated with CRL. This difference is statistically not significant, but CRL has significantly fewer side-effects than morphine. The present data do not permit a definitive judgement on the value of CRL in the treatment of tumor pains. Further studies with more patients and different doses and administration routes are warranted.