The ST2 gene encodes receptor-like molecules that are very similar to the interleukin-1 receptors. Three types of ST2 gene products, ST2, ST2L, and ST2V, can be produced by alternative splicing. In the course of cloning the chicken ST2 and ST2L cDNAs, we identified a novel variant cDNA other than ST2, ST2L, or ST2V, and tentatively named it ST2LV. ST2LV was produced by alternative splicing that deleted the transmembrane domain of ST2L. The chicken ST2 gene consisted of 13 exons and had two promoters followed by noncoding exons 1a and 1b, like the ST2 genes of human, mouse, and rat. The chicken ST2 mRNA was detected by RT-PCR as early as embryonic day 5. After that, the chicken ST2 mRNA was expressed in all examined organs, including the brain, eye, heart, lung, and liver. The chicken ST2LV mRNA was detected from embryonic day 10. The chicken ST2LV cDNA was transiently expressed in COS-7 cells. A protein of 69 kDa was detected in the culture supernatant, and the size of the protein was reduced to 53 kDa by treatment with peptide-N-glycosidase F, which suggested that ST2LV is a new soluble secreted and N-glycosylated variant of the ST2 gene product.