Proper development of metazoan embryos requires cell to cell communications. In many instances, these communications involve diffusible molecules, particularly members of the Transforming Growth Factor beta superfamily. In an effort to identify new members of this superfamily involved in the control of early zebrafish embryogenesis, we have isolated a gene, Radar, which appears to be conserved throughout vertebrate evolution and defines a new subfamily within the superfamily. Its pattern of expression suggests that Radar plays a role in the dorso-ventral polarity of the neural plate, blood islands formation, blood cells differentiation, the establishment of retinal dorso-ventral polarity and/or proper axonal retinotectal projections. Radar expression in ntl homozygous mutants indicates that notochord and hypochord development are intimately linked.