Previous studies have shown that in adult male mice, expression of the meg1 gene is restricted to meiotic and early postmeiotic testicular germ cells. We have now analyzed the expression of meg1 during postnatal testicular development and the comparable meiotic stages in the female. The 0.75 kb transcript for meg1 begins to accumulate in testes at d8-9 of postnatal (pn) development, coincident with the entry of germ cells into meiosis, and is expressed most abundantly at pn d14 and subsequent stages, when the spermatocytes have entered pachytene. In situ hybridization analysis shows that meg1 is expressed at very low levels in leptotene cells and increases as the cells progress through zygotene and pachytene stages. In the embryonic ovary, meg1 is not detected until after day 15 of gestation when the cells have entered the pachytene stage of meiosis I. In situ hybridization analysis suggests that meg1 transcripts are expressed at higher levels in degenerating rather than in healthy pachytene stage oocytes; meg1 is not expressed in any cells of the adult ovary, regardless of the stage of follicular development. These results suggest that meg1 is indeed a meiosis-associated gene in both male and female germ cells through the pachytene stage of meiosis I and appears to exhibit sex-specific differences in its expression thereafter.