The purpose of this study was to identify alternative life and physical science concepts possessed by preservice elementary science teachers (n=49). Science textbooks used in grades 5 and 6 were surveyed and a literature review of alternative life and physical science concepts was conducted. Results of the survey and literature review resulted in a pool of 12 life science concepts and 8 physical science concepts. Based on these results, two open-ended questionnaires were constructed to probe teachers' understanding of the concepts they were expected to understand to be able to teach. A content analysis of the responses was then used to develop pilot versions of the Life Science Misconceptions Test and Physical Science Misconceptions Test. Administration, scoring and further analysis of the results of the pilot versions of the tests revealed that subjects possessed a total of 36 life science misconceptions and a total of 50 physical science misconceptions. Details of the misconceptions identified are presented. (Author/CW)