Four experiments were conducted with Japanese children and adult participants to assess their awareness of the effectiveness of biological and psychological treatments for psychogenic bodily reactions. Study 1 had 116 participants, composed of 4-year-olds (17), 5-year-olds (20), 7-year-olds (24), 10-year-olds (20), and college students (35). The preschoolers tended to respond that only biological cures were effective in treating psychogenic bodily reactions, whereas adults typically responded that only psychological cures were effective. In Studies 2-4, by modifying the wording of the questions, adults' and young children's awareness was reexamined. As a result, in Studies 2 and 3, Japanese adults frequently acknowledged the effectiveness of biological treatments, and, in Study 4 (32 five-year-olds and 34 seven-year-olds), about 70% of the 5-year-old preschoolers who were aware of psychogenic bodily reactions tended to respond that psychological cures were effective in treating these psychogenic reactions. The results were discussed in terms of the developmental course in cross-domain awareness (i.e., reasoning about phenomena that cross ontological domains) and cultural differences in biological understanding. (Contains 1 figure and 4 tables.)