Stem cells given in the vital period immediately after a stroke may aid recovery, suggest researchers.
Rats injected with stem cells 30 minutes after a stroke had almost normal brain function restored within a fortnight.
The Bolivian research team say the method has potential in human trials.
Current best practice is to treat many patients with "clot-busting" drugs in the "golden hour" after a stroke has taken place.
The research, published in the journal Stem Cell Research and Therapy, adds to others which have found that stem cells could aid stroke patients by boosting the body's ability to repair tissue damage.
Stem cells are the body's "master cells", with the potential to become many different cell types, and theoretically replace cells lost through disease or injury.
Recent tests in humans have show some promise, with stroke symptoms improving after an infusion of stem cells.
The Bolivian team, from La Paz University Hospital, extracted a certain type of stem cells from fat and bone marrow, then injected them into the blood vessels of rats shortly after they had suffered an artificially-induced stroke.
Even though the introduced cells did not appear to travel to the affected region of the brain, the rats still did better than other rats who did not receive the cells.
Within 24 hours, they were already showing a speedier recovery, and two weeks later, they registered almost normal scores on behavioural tests.
Easy to use
The researchers said the early introduction of the cells might even interrupt the typical "chain reaction" of tissue damage which follows a stroke, in which the initial injury harms additional cells in surrounding areas.
Dr Exuperio Diez-Tejedor, who led the research, said: "Improved recovery was seen regardless of origin of the stem cells, which may increase the usefulness of this treatment in human trials.
"Adipose (fat) -derived cells in particular are abundant and easy to collect without invasive surgery."
The ease of collection, and the ability to use "allogenic" cells from other rats rather than having to harvest the animal's own cells and culture them, meant a treatment was available not weeks after a stroke, when the damage was done, but in this case minutes.
They wrote: "From the viewpoint of clinical translation allogenic stem cells are attractive because they can be easily obtained from young healthy donors, amplified, and stored for immediate use when needed after a stroke."
They suggested that it might be possible to overcome the risk of immune rejection of the donor cells in humans.
However, a spokesman for the Stroke Association said that human trials of this particular technique would not be possible in the near future.
Dr Clare Walton said: "Stem cells are an incredibly interesting area of stroke research and the results of this study provide further insight into their potential use for stroke recovery.
"However, we are a long way off these types of treatments being used in humans and a lot more research is needed."