Ovine and bovine trophoblast protein-1 (oTP-1 and bTP-1) have been strongly implicated as antiluteolytic agents and responsible for maternal recognition of pregnancy in sheep and cattle, respectively. Both are interferons (IFN) belonging to the IFN-alpha family, but their length (172 residues versus 166 for most IFN-alpha) places them in an unusual subclass (the IFN-alpha II). The various isoforms of oTP-1 and bTP-1 produced by trophoblast tissue appear to arise in part from translation of multiple mRNAs which are themselves the products of distinct genes. These genes, like those for other IFN-alpha, are without introns. However, the genes for oTP-1 and bTP-1 form a distinct subgroup within the IFN-alpha II on the basis of their overall primary sequences and the high conservation of the 3'-untranslated ends of their transcription units. The bTP-1 genes also differ from the bovine IFN-alpha II in the organization of the promoter regions upstream from the transcription start site. Nevertheless, computer-aided analysis of the primary polypeptide sequences of oTP-1 and bTP-1 indicates that the molecules are likely to have approximately the same shapes and dimensions as all other IFN-alpha molecules. It remains to be determined whether they have unique biological properties which distinguish them from other IFN-alpha molecules.