The General Motors Dexron-II automatic transmission fluid specification, issued in August 1973, defines physical, chemical, and performance requirements of a new class of fluids developed to meet increasingly severe service in passenger car and commercial automatic transmissions.Four new tests for determining fluid performance and durability have been developed for the specification. Results from these tests with Dexron-II prototype fluids are compared to those with Dexron fluids. It was found that the prototype fluids are much more oxidation-resistant than typical fluids in the Turbo Hydra-matic oxidation test; a 60% improvement in fluid durability has been realized in the Turbo Hydra-matic transmission cycling test; and Dexron-II prototype fluid friction and wear characteristics are about equivalent to those for Dexron fluids in the high energy, friction characteristics and durability test, and the wear test. Fluid deterioration in the transmission tests was determined from shift times, transmission cleanliness, increases in fluid total acid number and infrared carbonyl absorbance, and the oxygen concentration decrease in the transmission gas. Tests were repeatable, and results correlated with those obtained in service.The application of Dexron-II-quality fluids in hydraulic equipment and the General Motors gas turbine and rotary engines is reviewed.