To explore the relationship of four sets of factors on Mexican American and Anglo American students' desire to take science courses (enjoyment of science, grades, importance of science, and self image), data were gathered from ninth grade students at three high schools in southern Arizona, by using questionnaires for students and interviews with parents and teachers. Analyses compared the pattern of association between the variables in each sex and ethnic group to determine whether different factors were related to taking science or if the same factors were involved but the strength of the relationships varied by sex and ethnicity. Results indicated that Anglo males had a greater interest than females or Mexican American males in taking science courses, and that Mexican Americans were more influenced by affective orientation toward science than Anglos. Suggestions were: better career education as a means of increasing students' awareness of science careers and the importance of learning science for a variety of occupations; changes in the science curriculum to strengthen applicability of course material to occupations and to understanding the world; and further research on factors contributing to ethnic differences in science grades (e.g., improvement in basic skills for Mexican Americans where necessary). (AN)