Signaling molecules belonging to the Fibroblast growth factor (Fgf) family are necessary for directing bud outgrowth during tracheal development in Drosophila and lung development in mouse. A potential inhibitor of the Fgf signaling pathway, called Sprouty, has been identified in Drosophila. We have identified three potential mouse homologues of sprouty. One of them, called Sprouty4, exhibits a very restricted expression pattern. At 8.0 dpc (days post coitum) Sprouty4 is strongly expressed in the primitive streak region. At 9. 5 and 10.5 dpc, Sprouty4 is expressed in the nasal placode, the maxillary and mandibular processes, the otic vesicule, the second branchial arch, in the progress region of the limb buds and the presomitic mesoderm. Sprouty4 expression is also detected in the lateral region of the somites. In the developing lung, Sprouty4 is expressed broadly in the distal mesenchyme.