Tentacle formation in hydra involves three steps: the specification of body column tissue for the tentacle zone; commitment of spots in this zone to tentacle formation; and, finally, tentacle formation itself. On p. 2225, Takahashi and co-workers reveal that the peptide Hym-301, which was isolated in a screen for peptides regulating hydra development, is involved in controlling the second of these steps. The researchers show that the gene encoding Hym-301 is expressed in the ectoderm of the tentacle zone in adults and in the developing head during bud formation and head regeneration. Treatment of regenerating heads with Hym-301 or with Hym-301 dsRNA alters the number of tentacles formed. These and other results indicate that Hym-301 is involved in axial patterning in hydra and raise the possibility that this and other peptides that affect patterning in hydra may also act as signalling molecules in bilaterians.