Whilst insulin is a spectacularly successful drug for the management of diabetes mellitus, it remains difficult to mimic the physiological pattern of insulin secretion, even using the various quick-acting and insoluble formulations that are available. The introduction of recombinant-DNA technology to the manufacture of therapeutic insulin has made the rational design and production of insulin analogues with altered pharmacokinetic and pharmacological properties possible. Such analogues include 'monomeric' insulins, which do not form the insulin-zinc hexamer in solution and are absorbed more rapidly from the injection site, and long-acting insulins, which are absorbed very slowly at physiological pH. Many of these analogues are being tested clinically, and it is possible that the next generation of insulin therapy will be various combinations of rationally designed insulin analogues produced by industrial biotechnology.