Transcription mediators are evolutionarily conserved from yeast to human. We previously reported the specific in vivo roles of mediators during development. Transcriptional mediators including med-6, med-7, and med-10 were shown to be involved in the regulated transcription of specific genes, but not in the transcription of ubiquitous genes. In this report we have identified and characterized the Caenorhabditis elegans med-7 gene. A genetic mutation in the med-7 gene was identified by comparing genetic and physical maps and determining the molecular lesion. let-49 was found to have a nonsense mutation in the coding region of the med-7 gene. The identification of let-49 as the med-7 gene was confirmed by rescue experiments. The phenotype of the let-49 mutation indicated that the med-7 gene is required for normal postembryonic development. RNAi experiments showed that med-7 is also involved in embryogenesis and the gonad and germ cell development.