Research was conducted to develop and test a structured interview format questionnaire for assessing the vocational decision-making capacities and deficits of vocational rehabilitation clients. Eighty items were developed which tapped three broad domains of problem areas that clients may have in making vocational decisions--problems of information, environmental problems, and problems in making actual decisions. These items were subjected to content validation procedures, using experts in the field. The resulting vocational Decision-Making Interview (DMI) was then field tested with vocationally undecided clients, vocationally decided clients, and a group of vocationally mixed high school students. Reliability studies showed the instrument to be adequate, while concurrent validity studies with the Career Maturity Inventory-Attitude Scale showed that only one subscale of the DMI failed to correlate significantly with the criterion. Further, data for discriminant validity showed that on DMI total score and two of the three subscales the instrument discriminated significantly between clients who are vocationally decided and vocationally undecided. The newly developed DMI appears to hold promise to the field of vocational rehabilitation as an instrument for determining the vocational decision making problems and deficits of vocational rehabilitation clients. (Author/KC)