Some of the 40 frogs and toads returned last month already had the chytrid fungus blamed for wiping out dozens of frog and amphibian species.
The Smithsonian Institution's National Zoo in Washington is leading the effort with six other zoos and institutes as part of the Panama Amphibian Rescue and Conservation Project. The researchers are announcing their findings Friday.
They are planning a second, urgent expedition next week to hunt for more healthy frogs.
Brian Gratwicke, the Smithsonian's lead scientist on the project, has said half of all amphibians could go extinct because of the fungus.