A process for the production of a peptide is disclosed, the process comprising expressing in the milk of a transgenic, non-human, placental mammal a fusion protein which comprises the peptide to be expressed linked to a fusion partner protein which is lysozyme. The fusion protein may be separate from the milk and cleaved to yield the target peptide. A transgenic, non-human, placental mammal whose genome incorporates a DNA molecule comprising a coding sequence encoding lysozyme coupled to a peptide is also described.