The present study: (1) identified certain scientific misconceptions possessed by high school and university students; (2) identified, by written and interview means, the origins of these misconceptions; and (3) classified the misconceptions according to their origin. A pilot study using grade 9 high school students showed that, although more time-consuming, a clinical interview yielded more information about the origins of misconceptions than a request for written information about the origins. A final instrument, the Trembath Test of Scientific Misconceptions (TTSM) consisting of 16 true/false items, 15 multiple choice items, and 6 brief written statements, was administered to 47 college students. The TTSM was shown to have a satisfactory reliability. The validity of the test was measured by sampling techniques and by the judgments of a group of science educators. A clinical interview technique revealed the origin of 97.7% of the misconceptions that were detected. The number of semester hours of science taken at grade 10 level correlated positively with the number of misconceptions possessed, and the number of credit hours of science taken in upper division of college correlated negatively with the number of misconceptions possessed. (Author/DS)