This was a randomized (patients are assigned different treatments based on chance), open-label, four-way crossover study performed in normal, healthy adult patients. Each patient received the following orally administered treatments of OROS® Hydromorphone HCL (a different treatment during each dosing phase): Treatment A: 8mg; Treatment B: 16mg; Treatment C: 32mg; Treatment D: 64mg; A naltrexone 50mg dose was administered 12 hours prior to, at the time of, and 12 after study drug administration; Patients received a fourth dose of naltrexone 50mg 24 hours after the 64mg study drug administration. There was a 7-day washout period between study drug dosing phases.Venous blood sampling times were 0 (prior to dosing), 2, 4, 6, 8, 10, 12, 16, 20, 24, 30, 36, 42, and 48 hours after each study drug administration. Three additional blood samples (at 56, 64, and 72 hours after dosing of study drug) were drawn from those patients receiving the 64 mg tablets; LC/MS/MS (Liquid Chromatography/Mass Spectroscopy/Mass Spectroscopy) techniques were employed for the analysis of plasma hydromorphone concentrations.The primary endpoints of interest were: Area under the concentration-time curve from zero to infinity; Area under the concentration-time curve from zero to time t; Peak plasma concentration; the secondary endpoint parameters were: Time to peak plasma concentration; Terminal half-life. OROS hydromorphone HCL tablets of 8mg, 16mg, 32mg, and 64mg were given orally, a different dosing treatment during each dosing phase. One naltrexone HCL 50mg tablet was given orally 12 hours prior to, at the time of, and 12 hours after hydromorphone administration during each dosing phase. Patient received a fourth dose of naltrexone 50mg 24 hours following the 64mg study drug administration; It was a four week treatment and there was a seven-day washout period between dosing phases.