Dr. Craig Spencer, who is in isolation at Bellevue Hospital, received plasma treatments Saturday, when doctors said his illness had entered a "more serious, but expected stage."
"He tolerated the plasma treatment which was given to him yesterday well, and he had a good night's sleep," Ram Raju, head of the city's Health and Hospitals Corporation, said.
Health officials did not identify the source of the plasma, but the aid agency SIM Charity told ABC news that health worker Nancy Writebol, who survived Ebola she contracted in Liberia, donated blood to Spencer.
New York City Mayor Bill de Blasio said he spoke with Spencer for 10 or 12 minutes by phone on Saturday.
"This is an incredible noble human being," the mayor said. "He ran towards the danger to protect the entire world."
Spencer, 33, had been treating Ebola patients in Guinea until Oct. 12, New York City Department of Health Commissioner Dr. Mary Bassett said. Spencer left Guinea on Oct. 14 and arrived at New York's John F. Kennedy International Airport on Oct. 17 following a stopover in Brussels, Belgium.
Doctors Without Borders Guidelines requires doctors like Spencer to take their temperature twice a day and to stay within four hours of a hospital for the 21-day incubation period. They are also supposed to contact Doctors Without Borders if they developed any symptoms.
On Thursday morning, Spencer recorded a temperature of 100.3 and called Doctors Without Borders, who contacted New York authorities. Emergency responders arrived at his northern Manhattan apartment in full protective gear and took him to Bellevue, where he was placed in isolation and later diagnosed with Ebola, according to officials.
Spencer's fiancee and two friends who were determined to be at risk of having contracted the disease from him have also been quarantined in their homes until Nov. 14, city health officials said.