Desirable fusion proteins can be produced in and purified from the milk of transgenic animals. The peptides are made as fusion proteins with a suitable fusion partner such as human alpha-fetoprotein. The fusion partner protein acts to promote and increase the half-life of the overall molecule as well as having therapeutic effects on its own. The fusion protein is typically produced through the use of transgenic animals and can be purified away from the now the milk or other bodily fluid of such an animal by an affinity purification method. A particular advantage of producing peptides via this route, in addition to the obvious advantages of high yield and biocompatibility, is that specific post-translational modifications, such as carboxy terminal amidation, can be performed in the mammary gland. Biologically active polypeptides comprising a therapeutically active polypeptide fused to human alpha-fetoprotein fragment or a variant thereof, methods for the preparation thereof, nucleotide sequences encoding such fusion polypeptides, expression cassettes comprising such nucleotide sequences, self-replicating plasmids containing such expression cassettes, and pharmaceutical compositions containing said fusion polypeptides.