The appropriateness of a testing is necessary for test results to be reliable and valid. The participant should not feel a high degree of discomfort during the research as it will affect one’s behavior and opinion and therefore the obtained informations. The Autism Diagnostic Observation Schedule contains five modules, of which Module 4 is used for administration with verbally fluent adolescents and adults. The aim of this paper was to examine the material appropriateness of the fourth module of the Autism Diagnostic Observation Schedule (ADOS-2; Lord et al., 2012) on adults in the Republic of Croatia. For this purpose, a questionnaire was prepared by the examiner to assess the appropriateness and degree of comfort of the materials and questions used during the implementation of ADOS-2. Participants were 40 adults of typical development, aged 35 to 50, who are native speakers of Croatian language and who have spent all their lives in the Republic of Croatia. The results showed that most of the materials used were appropriate for the age at which they were used, but also that there were indications for additional material verification and for the possible disposal of certain activities and materials. Tasks like ‘Telling a story from a book’, ‘Construction task’ and ‘Description of a picture task’ show a lower level of appropriateness. The lowest levels of comfort are demonstrated by: ‘Demonstration Task’, ‘Break’ and ‘Telling a story from a book’. Although literature mostly indicates that the materials and questions used during the protocol testing are appropriate for adulthood, this research shows that certain specific materials should be further verified in order to make the Module 4 trial itself more valid.