The SPARC family consists of several proteins (SPARC, hevin, fstl-1, testican 1/2/3, SMOC1, and SMOC2) and all members contain an extracellular calcium binding (EC) domain with 2 EF hands and a follistatin-like (FS) domain (Alliel et al., 1993 Charbonnier et al., 1998 Vannahme et al., 1999, 2002, 2003 Brekken and Sage, 2001 Hambrock et al., 2003, 2004 Schnepp et al., 2005). SMOC2 is a member of the BM-40/osteonectin/SPARC ( Secreted Protein Acidic and Rich in Cysteines) family of secreted proteins that do not contribute to extracellular matrix structures but rather regulate cell-matrix interactions (Bornstein, 2000). Furthermore, our data show that Smoc2 affects the transcription of Bmp target genes without affecting initial dorsoventral patterning or mesoderm development. Conclusions: Our findings reveal that Smoc2 is an essential player in the development of myeloid cells of the anterior lateral plate mesoderm during embryonic zebrafish development. Additional experiments indicated that Bmp target genes were down-regulated in smoc2 morphants. Hemangioblast development and further specification of the myeloid progenitor cells were shown to be impaired. Molecular analysis of the smoc2 morphants indicated myelopoietic defects in the rostral blood islands during segmentation stages. At the onset of blood cell circulation, smoc2 morphants presented a mild ventralization of posterior structures. As development progresses, the expression pattern becomes more anteriorly restricted. Results: In pregastrula zebrafish embryos, smoc2 is expressed ubiquitously. The function of Smoc2 during early zebrafish development has not been determined to date. Additionally, SMOC2 is associated with vitiligo and craniofacial and dental defects. In mice, Smoc2 is expressed in many different tissues and was shown to enhance the response to angiogenic growth factors, mediate cell adhesion, keratinocyte migration, and metastasis. Background : SMOC2 is a member of the BM-40 (SPARC) family of matricellular proteins, reported to influence signaling in the extracellular compartment.