The influence of variations in beryllium content on the mechanical properties of copper-beryllium alloy strip is discussed. Four tempers of each of five alloys varying in beryllium content from 1.60 to 2.05 per cent were investigated, both in the solution heat-treated and strain-hardened conditions and after precipitation heat treatment. The mechanical properties evaluated include tensile strength, proportional limit, 0.01 and 0.2 per cent offset yield strengths, modulus of elasticity, elongation, fatigue strength in reversed bending at cycle lives ranging from 105 to 168, Rockwell and Rockwell superficial hardness. The effect of surface treatments on fatigue life, including furnace atmospheres and shot peening, is shown. Hardness response curves are given for the five alloys for various periods of time ranging from 1/2 to 5 hr at temmperatures of 575 to 700 F in increments of 25 F. From these studies the correlation between Rockwell B and Rockwell 30T hardness values, and Rockwell C and Rockwell 30N hardness values for each of the alloys was established. Data are also presented showing the resistance of the two commercial copper-beryllium alloys (No. 25 and No. 165) to stress corrosion cracking.