qRT-PCR analysis of human fetal gonads reveals female-biased and developmentally-regulated expression of STRA8 (A). STRA8 expression increased significantly between 8–9 and 14–16 weeks in the human fetal ovary (a vs b, p<0.05) consistent with the initiation of meiosis in the fetal ovary around 11 weeks gestation. Levels of transcripts encoding STRA8 were low and not significantly different between human fetal testes and ovaries at 8–9 weeks gestation, but were significantly higher in fetal ovaries than fetal testes at 14–16 weeks (c vs d, p<0.0001) and 17–20 weeks (e vs f, p = 0.008). CYP26B1 (B) expression was not significantly different between samples of the same sex at different gestational ages, but was significantly higher at in the fetal ovary than the fetal testis at 14–16 weeks (a vs b, p = 0.02); suggesting the male-specific expression of CYP26B1 reported in mice at a comparable developmental stage is not conserved to humans. NANOS2 (C) expression was predominantly male-specific and developmentally-regulated, with expression increasing in the human fetal testis with increasing gestational age (a,b,c, p<0.001). NANOS2 expression was also significantly higher in fetal testes than ovaries at 14–16 weeks (d vs e, p = 0.01) and 17–20 weeks (f vs g, p<0.01), a result consistent with a role for this protein in repressing meiosis in the fetal male germline. 8–9, 14–16 and 17–20 denote gestation age (in weeks) of specimens. No differences were detected in the expression of NANOS1 (D) between testis and ovaries at any gestational age, nor between gonads of the same sex at any developmental stage. NANOS3 expression (E) was significantly higher in the human fetal ovary at 14–16 weeks gestation than at 8–9 weeks gestation (a vs b, p<0.05), in contrast to the downregulation of the homologous gene in the fetal mouse ovary at the comparable developmental stage. Expression of NANOS3 was also greater in the fetal ovary than in the fetal testis at 14–16 weeks (c vs d, p<0.05) and 17–20 weeks (e vs f, p<0.02). 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens, values denote mean ± s.e.m, 8–9, 14–16 and 17–20 denote the gestational age (in weeks) of specimens.