That would be the blood of people who have been sickened by the Ebola virus but have since recovered. Their blood should contain antibodies that might help other patients fight off the infection.

The World Health Organization is making it a priority to try such convalescent blood or plasma, as it is called, and is talking with the affected countries about how to do it.

This week, the organization issued guidance on how to collect the blood and administer transfusions.

“The concept that this treatment could be efficacious is biologically plausible, as convalescent plasma has been used successfully for the treatment of a variety of infectious agents,” the W.H.O. guidance document says.