Inclusion Criteria:

- Subjects with CD20 and CD22-positive, follicular or diffuse large B-cell NHL who have
not responded or progressed after 1 or 2 prior therapies; or subjects with CD20 and
CD22-positive intermediate/aggressive NHL (diffuse large B-cell, mantle cell,
transformed follicular or follicular grade 3b NHL) who have not responded or
progressed after 1 or more prior therapies and are refractory to a previous rituximab
containing therapy.

- Prior therapy must contain at least one course of rituximab therapy, as single agent
or in combination.

- Measurable disease.

Exclusion Criteria:

- Subjects who are candidates for other potentially curative therapies.

- Subjects must not have received previous radioimmunotherapy.

- Subjects who have undergone a prior bone marrow transplantation within the last 6
months.