Inclusion Criteria:

Phase I and Phase II portions of the study:

- 18 years of age or older

- Chronic pain with average 24 hour intensity rated at least 3 on a verbal numerical
scale from 0-10 during the 24 hours prior to study entry.

- Give informed consent to participate in this study.

- Karnofsky Performance Score (KPS) >= to 80

- Negative urine pregnancy test, verified by the study nurse, at study entry (for women
of child-bearing potential). Patients must also use a medically approved
contraceptive method during the study period.

Phase I only:

- Responsible companion living with patient during study.

Phase II only:

- Group 1 -- Patients must be taking chronic opioid therapy (long acting morphine, long
acting oxycodone, transdermal fentanyl) at a stable dose for a minimum of four days.
The dose of as needed short acting opioid does not need to be stable.

- Group 2 -- Patients must not be receiving opioids and must have cancer related
neuropathic pain secondary to post-chemotherapy peripheral neuropathy, post-radiation
and/or post surgical plexopathy, radiculopathy or neuropathy, or post- herpetic
neuralgia.

Exclusion Criteria:

Phase I and Phase II:

- Known hypersensitivity to methadone

- Patient taking methadone or with a history of methadone treatment within one month of
study enrollment.

- Patient that requires changes in the dose of one of the following medications within
2 weeks of study enrollment:

- Abacavir,

- Benzodiazepines,

- Carbamazepine,

- Efavirenz,

- Fluconazole,

- Fluvoxamine,

- FOS amprenavir,

- Fosphenytoin,

- Naltrexone,

- Nelfinavir,

- Nevirapine,

- Phenytoin,

- Rifampin,

- Rifapentine,

- Risperidone,

- Ritonavir,

- St. John's Wort,

- Zidovudine

- Hepatic function tests (SGOT, alkaline phosphatase, bilirubin) greater than 2 times
the upper limit of normal or creatinine greater than 1.4 within 30 days of study
entry.

- Neurologic or psychiatric disease sufficient, in the investigator's opinion, to
compromise data collection.

- Women who are pregnant or nursing.

- Women of childbearing potential who do not agree to use a medically recognized method
of contraception during the study period.