Synopsis The paper examines the influence of mix parameters upon the strength and deformation of plain concrete subjected to uniaxial tensile or compressive stress. Parameters considered are the effective water/cement ratio, aggregate/cement ratio, aggregate maximum size and grading defined in terms of mean particle size, and the strength, elastic modulus and crushing value (B.S. 812) of the coarse aggregate. Tensile and compressive strength, tensile strain at failure and compressive strain at 50 % compressive strength are related to each parameter in turn, often by expressing the values in relative terms. The results obtained from 94 mixes are used to develop charts which permit reasonably accurate prediction of any of the four properties listed above for a wide range of mixes.