The fibroblast growth factor (Fgf) signalling pathway has a conserved and essential role in the development of posterior mesoderm in vertebrates. While Fgf8 accounts for most of the Fgf signalling needed for this process in mice, zebrafish fgf8 mutants have only mild defects in posterior mesodermal development. On p. 4639, Draper et al. report that both fgf8 and the newly identified fgf24 are required for the development of posterior structures in zebrafish. They show that fgf24, an fgf8-related gene, is co-expressed with fgf8 in mesodermal precursors during gastrulation. Inhibiting fgf24 alone through morpholino-based gene inactivation did not affect the formation of posterior mesoderm in normal embryos but blocked this tissue's formation in fgf8 mutants. The authors also show that fgf8 and fgf24 probably interact with no tail and spadetail,zebrafish T-box transcriptional factors that are required for posterior body formation.