A system usinga vibratory probe oscillating in close proximity to a specimen surface was improved in order to study the effects of tensile stress on the initial stages o f cavitation damage: the temperature distribution on the stationary specimen came within f 0.3 "C, and the errors in the experimental results were able to be kept below f 3%.A tensile stress applied on such ductile metallic materials as aluminum, iron (ferrite) and mild steel inhibits cavitation damage in the early stage: the incubation period was extended to a maximum of five times. However, the damage is accelerated in the stage affected with weight loss. A n applied tensile stress on such brittle material as cast iron accelerates damage both in the incubation period and the following periods of damage.of tensile stress on cavitation damage has been discussed.The mechanism o f these favorable and unfavorable effects