Immunoexpression of OCT4, DAZL and VASA. OCT4 positive germ cell nuclei were detectable in both the 1st and 2nd trimester ovaries (a, 62 d; b, 16 wk) and testes (c, 64 d; d, 16 wk). DAZL positive germ cells were rare in the 1st trimester (e, ovary 61 d; g, testis 64 d) but groups of cells ('nests', labelled N) with cytoplasmic staining were present in the 2nd trimester ovaries (f, 20 wk). During the 2nd trimester VASA protein was detected in the cytoplasm of female germ cells (i, 14 wk; j, 18 wk) throughout the ovary with the exception of the sub-epithelial layer. In the testes (k, 15 wk; l, 16 wk) VASA-positive germ cells were found in all cords.