Most existing treatments for depression target levels of brain chemicals, such as serotonin and dopamine, and, over time, the accumulation of these chemicals can affect a patient's mood but this may take weeks or even months to work properly.
However, the research team, writing in Archives of General Psychiatry, said ketamine would need to be altered so it no longer had hallucinatory side effects.
Scientists from NIMH injected 17 patients with either a very low dose of ketamine or a placebo of saline solution and the researchers then measured their levels of depression minutes, hours and days after the dose was given.
All the participants suffered from depression and had tried an average of six treatments before that had failed.
Lead researcher Dr Carlos Zarate Junior, head of the mood and anxiety disorders programme at NIMH, said: "Within 110 minutes, half of the patients given ketamine showed a 50% decrease in symptoms."
By the end of day one, Dr Zarate added, that 71% had responded to the drug and at this point the team found 29% of these patients were nearly symptom free.
The scientists believe ketamine is having a faster effect because it is targeting a different brain-protein, called the NMDA receptor, which is considered to play an important role in learning and memory.
Unfortunately, at present ketamine would not be suitable as an antidepressant medication because of the side-effects at higher doses, which can include hallucinations.
