On the basis of some fundamental principles for the design of fly ash concrete mixes,1,2 the Author proposes a number of modifications and extensions of the British DOE method for the ‘Design of normal concrete mixes’. The suggested modifications make it possible to extend use of the DOE method to design of wet lean concretes and controlled low strength materials (CLSM). The properties of both these types of concrete are con-siderably improved by the addition of high volumes of fly ash, but it requires some skill to design high volume fly ash concretes in a logical manner, so that they do show the optimum properties both in the fresh and the hardened state.