The Oak Ridge National Laboratory has for several years been conducting tests relating to ultimate disposal of highly radioactive power reactor wastes in salt mines. A number of laboratory and field tests have been conducted on properties of salt which are important in the design and operation of a waste-disposal facility. In situ heat transfer properties are sufficiently close to the values determined in the laboratory that confidence can be placed in theoretical heat-transfer calculations. Most bedded salt contains trapped moisture which is released with violence at temperatures above about 250°C. Radiation exposure doses of 5 × 10 8 roentgens produce some changes in structural properties, but the effect on mine stability should be negligible. Rock salt is approximately equivalent to concrete as a gamma-radiation shield. Stability of a waste-disposal mine at ambient temperature can be predicted from observed conditions in existing salt mines. Elevated temperatures will cause accelerated creep, but the exact effects on structural stability cannot yet be predicted accurately.