The authors report a prospective study on 944 cancer pain patients treated with one of the following opioids: codeine, oxycodone, dextropropoxyphene, buprenorphine, and pentazocine. Level of analgesia, duration of treatment, side effects, and drop out were evaluated for each drug. Twenty-four percent of the patients still benefitted from treatment at the fourth week of study, even if high drug dosages were not used. Pentazocine did not show an evident analgesic effect during the first 2 wk of treatment. The other opioids were found to be valid therapeutic instruments for chronic cancer pain control in a limited number of patients.