Dsx and mab-3-related transcription factor (DMRT1), Protein kinase C inhibitor (PKCIW) and Female-specific expression transcription factor (FET1) have been regarded as critical candidates of avian sex determination. Their mRNA expression was analyzed in chicken embryos during experimentally induced female-to-male sex-reversal by an aromatase inhibitor (AI) fadrozole. DMRT1 expression was higher in male (ZZ) gonads than in female (ZW) gonad prior to and throughout the pe-riod of sex differentiation. However, female-to-male sex-reversed ZW embryos showed elevated levels of DMRT1 expres-sion similar to those of normal males, indicating that DMRT1 was associated with testis development. PKCIW gene expres-sion was dimorphic between male and female gonads, and was up-regulated in AI-treated female embryos. This finding might account for the specific effect of PKCIW, functioning via heterodimerization with PKCI during avian sex determina-tion. However, its elevated expression appeared to be insufficient to induce ovary development. On the other hand, FET1 expression was female-specific and unchanged in AI-treated female embryos. Results of present experiment suggested that DMRT1 is a determinant for testis development in birds.