• INCLUSION CRITERIA

Between the ages of 18 and 65 years, inclusive.

Subjects with relapsing-remitting or secondary progressive Multiple Sclerosis who have had more than 1 relapse within 18 months preceding study enrollment.

EDSS score between 1 - 6.5, inclusive.

Give written informed consent prior to any testing under this protocol, including screening/pre-treatment tests and evaluations that are not considered part of the subject's routine care.

Patients who have failed standard IFN-beta therapy.

To be eligible to proceed to the treatment phase of the study, subjects must have at least 2 Gd-enhancing lesions or greater in the 3 pre-treatment MRI scans (an average of at least 0.67 Gd-enhancing lesions per scan).

In patients with high inflammatory activity and high relapse rates it has been our experience that the requirement of steroid therapy for the treatment of relapses may prolong the baseline phase. In patients with high disease activity who require steroid therapy and quickly afterwards demonstrate disease activity again, the investigator retains the option to enroll patients with less than the stipulated baseline months in order to initiate daclizumab therapy as quickly as possible. Since treatment escalation would otherwise require therapy with mitoxantrone or cyclophosphamide, which both have substantial toxicity, this step is in the best interest of the patient.

EXCLUSION CRITERIA:

Diagnosis of primary progressive MS, defined as gradual progression of disability from the onset without relapses.

Abnormal screening/pre-treatment blood tests exceeding any of the limits defined below:

Alanine transaminase (ALT) or aspartate transaminase (AST) greater than two times the upper limit of normal;

Total white blood cell count less than 3,000/mm(3);

CD4+ count less than 320/mm(3);

Platelet count less than 80,000/mm(3);

Creatinine greater than 2.0 mg/dL.

Concurrent, clinically significant (as determined by the investigator) cardiac, immunologic, pulmonary, neurologic, renal, and/or other major disease.

Any contraindication to monoclonal antibody therapies.

Patients who are HIV+ since the effects of anti-Tac are not defined in these patients.

If prior treatment was received, the subject must have been off treatment for the required period prior to enrollment.

Prior treatment with any other investigational drug or procedure for MS.

History of alcohol or drug abuse within the 5 years prior to enrollment.

Male and female subjects not practicing adequate contraception.

Female subjects who are not post-menopausal or surgically sterile must be using an acceptable method of contraception. Acceptability of various methods of contraception will be at the discretion of the investigator. Written documentation that the subject is post-menopausal or surgically sterile must be available prior to study start.

Unwillingness or inability to comply with the requirements of this protocol including the presence of any condition (physical, mental, or social) that is likely to affect the subject's returning for follow-up visits on schedule.

Previous participation in this study.

Breastfeeding patients.