Because of their consistent presence in the work environment, co-workers have been identified as a potentially powerful resource available to provide support to employees with disabilities in supported employment programs. The "Co-worker Involvement Instrument" allows employment training specialists and job supervisors to estimate co-worker involvement with target employees after job placement. The items on the instrument assess physical integration, social integration, training, frequency of associating, appropriateness of associating, befriending, advocating, evaluating, and giving information. Studies have found the instrument to demonstrate good interrater and test-retest reliability. This paper includes a copy of the instrument, a glossary, and instructions for scoring co-workers and for scoring employment site demographics. (28 references) (JDD)