Methods of production of desired recombinant proteins, polypeptides and peptides are disclosed which utilise mammalian host cells engineered for autonomous and regulated growth in low cost protein/serum-free culture media. Preferred host cells express insulin or an insulin-like growth factor, and/or transferrin and are engineered so that addition of an inducer (e.g. ZnCl2 + CdCl2) halts growth and simultaneously induces the expression of the desired recombinant protein, polypeptide or peptide.