We have cloned and sequenced the complete proteincoding region of the pig PIT-1 gene. The pig PIT-1 gene is highly similar to the PIT-1 gene in other species (human, rodent, cattle). We also found some alternative forms of the pig PIT-1 gene. We have analyzed the protein function of the pig PIT-1 genes and one of its alternative forms; D3PIT-1. The functional studies showed that the pig PIT-1 protein can function normally at growth hormone (GH) and prolactin (PRL), whereas the pig D3PIT-1 protein cannot. These results imply that the pig PIT-1 gene is important in pig growth through regulation of GH and PRL gene expression, whereas its alternative forms might play different roles on PIT-1 target genes.