"The conclusion then is, as it is now, that PTSD does not qualify, given the 76-year definition of what a Purple Heart recipient is," said Geoff Morrell, the Pentagon press secretary.
He said Gates thought the issue was worth re-addressing when asked about it in Texas, but accepted the conclusion of the panel that reviewed the requirements for receiving the award.
"But I don't think anybody should assume that that decision is in any way reflective on how seriously we take the problem of PTSD in this department," he said.
"I think we will spend about a billion dollars on research, development, treatment, preventative measures. And I think you will see more and more money being spent to combat this very real problem that we are all terribly concerned with," he said.
About 300,000 service members who fought in Iraq or Afghanistan suffer from PTSD or major depression, the Rand Corporation estimated in a study in April.
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Image of US soldiers examining their damaged Humvee after an Improvised Explosive Device (IED) detonated on the vehicle, following a patrol in Baghdad in 2007, by David Furst.