The drug ZMapp, viewed as perhaps the most promising potential treatment for Ebola, seemed to prevent death from the disease in its first rigorous clinical trial, researchers reported on Tuesday.

However, they said, the results were not conclusive, probably because the Ebola outbreak in West Africa ended before enough patients could be enrolled in the study.

ZMapp rose to the top of the list of possible Ebola treatments during the outbreak in 2014 when two American aid workers working in Liberia seemed to make a rapid recovery after being treated by it. The drug was experimental, and there was almost none of it available, setting off a clamor for it among desperate patients and their doctors.

But not all the patients who received the drug survived, so researchers conducted a randomized clinical trial to find out if the drug was effective. It enrolled 72 patients, mostly in Sierra Leone, but also in Liberia, Guinea and the United States. All received the optimized standard of care treatment, such as intravenous fluids and maintenance of oxygen levels and blood pressure. Half were randomly assigned to also receive ZMapp.