Purpose: To evaluate the safety and efficacy of a new slow-release preparation of hydromorphone (SRH) in the treatment of cancer pain. Patients and Methods: Ninety-five adult patients from three Canadian Palliative Core Centers with no evidence of mental impairment received treatment for cancer pain with an oral opioid analgesic, After informed consent was obtained, patients underwent titration to a stable dose of immediate-release hydromorphone (IRH) for 48 hours, and were then randomized to receive IRH or SRH for 5 days in a double-blind basis, During day 6, a crossover took place, and patients received the alternate drug for 5 days, Pain intensity was assessed using a visual analog scale (VAS) and ordinal scale (OS), Side effects were assessed using VAS, Patients and investigators made a blinded global rating of efficacy a blinded final choice between SRH and IRH. Results: In 75 assessable patients, pain intensity of the VAS were (mean +/- SD) 27 +/- 21 and 1.3 +/- 0.6 on IRH, versus 29 +/- 21 (P = .13) and 1.3 +/- 0.6 (P = .19) on SRH, respectively, The total number of extra doses of opioids, global rating, and final blinded choice by both patients and investigators were not significantly different between IRH and SRH, Differences in side effects were not significant. Conclusion: Our findings suggest that SRH is as safe and effective as IRH in the treatment of cancer pain. (C) 1996 by American Society of Clinical Oncology.