Wnt proteins have been implicated in regulating growth and pattern formation in a variety of tissues during embryonic development. We previously identified Frzb-1, a gene which encodes a secreted protein with homology in the ligand binding domain to the Wnt receptor Frizzled, but lacking the domain encoding the putative seven transmembrane segments. Frzb-1 has recently been shown to bind to Wnt proteins in vitro, and to inhibit the activity of Xenopus Wnt-8 in vivo. We report now that mFrzb-1 and Wnt transcripts display both complementary and overlapping expression patterns at multiple sites throughout embryonic development. By Northern analysis, the expression of mFrzb-1 in the developing mouse embryo is greatest from 10.5 to 12.5 days postcoitum (dpc). In the early embryo, mFrzb-1 is expressed in the primitive streak, presomitic mesoderm, somites, and brain. Later, mFrzb-1 exhibits sharp boundaries of expression in the limb bud, branchial arches, facial mesenchyme, and in cartilaginous elements of the appendicular skeleton. We conclude from these experiments that Frzb-1 is expressed at a time and location to modulate the action of Wnt family members during development of the limbs and central nervous system.