A study used item response theory to examine the vocational interests of 2,709 high school students (1,436 males; 1,273 females) in Australia in relation to Holland's vocational interest typology (1973, 1985, 1997), which identifies six fundamental vocational types (realistic, investigative, artistic, social, enterprising, and conventional) that link interests and work environments within the ambit of personality. Participants completed a 24-item questionnaire. Partial credit analysis was used to determine the location of the four questions that made up each of the vocational scales. Infit mean squares centered on 1.0 and separability was satisfactory for all scales (0.85 to 0.99) except the investigative scale. The conclusion was that scales and items conformed generally to the measurement model. The analysis of items using a Rasch model provided new information on how individuals responded to items and the complexity of responses within interest categories. It was concluded that simple raw scores or summing scores may not offer a valid basis for assessment of interests. (Included are two tables and six figures that show the distances between rating scales on the six scales. Contains 15 references.) (YLB)