An investigation of the combined effects of slow strain rate testing and cathodic protection of Ni-Cu Alloy K-500 forgings was performed. The J-integral fracture toughness tests were performed in a modified screw-driven Instron testing machine with measured cross head travel speeds of 0.1, 0.013, and 0.001 mm/min (0.004, 0.0005, and 0.000 04 in./min). The IT compact specimens used were modified for use with direct current potential drop (DCPD) measurement of the crack lengths. Specimens tested at 0.1, 0.013, and 0.001 mm/min were in an air environment. Additional specimens were tested at 0.001 mm/min in a 3.5% NaCl solution with an applied cathodic potential of -1.0 V (SCE). The tests were monitored with a desk top computer data acquisition system that recorded load, load-line opening displacement (COD), DCPD, applied cathodic potential, and impressed current. These data were used to construct J-integral resistance (J-R) curves for all the samples. The J-R curves for all the specimens tested in air had appeared similar. The specimens tested in salt water with cathodic protection had significant reduction in J-integral toughness (JIc) to less than half the air value. Examination of the specimens' fracture surfaces revealed that the cathodic protection caused the fracture mode to change from dimpled rupture to intergranular fracture.