Transmission electron microscopy (TEM) disks of pure copper and copper alloyed with 5 atom% of either aluminum, manganese, or nickel have been irradiated at 25°C with 14-MeV neutrons. Vickers microhardness measurements were obtained as a function of fluence up to a maximum level of 2.2 × 10²¹ n/m². Measurements were made at two different values of indenter load (5 and 10 g) in order to facilitate correlations with high-load microhardness data. A simple antivibration test stand was designed which allowed reproducible microhardness results to be obtained independent of background vibrations down to indenter loads of 2 g. The radiation-induced microhardness change at both indenter loads scales linearly with the fourth root of neutron fluence following an incubation fluence. At a fluence of 2 × 10²¹ n/m², the microhardness is increased by at least 50% over the unirradiated microhardness value for all four metals. The alloys, in particular Cu-5 Mn, exhibited a shorter incubation fluence and a larger radiation hardening than pure copper. Estimates of the defect cluster density obtained from 10 g microhardness data are in good agreement with TEM observations obtained on these alloys by other researchers. The measured irradiation-induced microhardness change is about 40% less at an indenter load of 5 g than at an indenter load of 10 g for a fluence of 2 × 10²¹ n/m². This indicates that irradiation-induced changes in low-load microhardness are dependent on the indenter load; therefore any results which are obtained at low loads should be used with caution.