A method for the treatment and/or prophylaxis of diabetes mellitus, conditions associated with diabetes mellitus and certain complications thereof, in a mammal which method comprises administering an effective non-toxic and pharmaceutically acceptable amount of an insulin sensitiser and a biguanide antihyperglycaemic agent, to a mammal in need thereof and a pharmaceutical composition comprising an insulin sensitiser and a biguanide antihyperglycaemic agent.