We report here the expression of AmphiMdp in embryos and larvae. Faint AmphiMdp transcripts were first detected in the mesendoderm at the mid-gastrula stage and later in the somites of the early neurula. Expression remained in somites throughout the neurula and early larval stages and then disappeared from the somites starting with the most anterior somite and progressing posteriorly. At the 48-h larval stage, transcripts were detected in the developing tail bud. No transcripts were detectable in the somites of the 72-h larva. The result suggests that AmphiMdp is involved in myogenesis in amphioxus.