Primary males that function as males throughout their lives are often found among protogynous fishes such as wrasses and parrotfishes. However, the issue of whether the sexuality of primary males involves gonochorism or hermaphroditism remains uncertain. To clarify this, we implanted estradiol-17β (E2) into the body cavities of primary males of two protogynous wrasses, Halichoeres poecilopterus and Halichoeres tenuispinis. At 51–63 days after implantation, primary males with E2 treatment in both wrasses were observed to develop ovarian tissues. These results suggest that primary males of Halichoeres wrasses potentially have the ability to change sex and that estradiol-17β is related to gonadal transitions in primary males.