The journey back to an operating theatre may still be the greatest obstacle to an astronaut who is seriously injured, or falls badly ill during a mission.
However, subtle changes to their body chemistry caused by space flight may place them at greater risk if they undergo medical treatment back on Earth.
The two monkeys were part of the joint Russian-American Bion 11 mission in 1997, flying aboard the space shuttle.
When they returned to Earth, the monkeys were given a general anaesthetic on the first day.
One monkey died and the other suffered serious complications, and a report on what might have caused this is being prepared by NASA.
Ronald Merrell, of the Medical College of Virginia in Richmond, who chaired the Bion task force for NASA, said: "The events could be explained if there was inadequate blood flow under anaesthetic, similar to that seen in a diabetic with severe nerve disorder."
Normally people take at least a day to regain complete control over their blood flow on returning to Earth.
Other potential health problems associated with weightlessness include bone thinning, as the bones do not need to be as thick to support the body, and weakening of the heart muscles, as pumping the blood is much easier at zero G than under normal gravity.
Poor first aid equipment
And other investigations have revealed that some of the first aid equipment used on space missions may be totally inappropriate for use in a weightless environment.
If a patient has stopped breathing, and a tube needs to be inserted, the astronauts have some training in how to use an endotracheal tube and laryngoscope.
However, some force has to be applied as the tube is pushed in, and experiments underwater in a mock "weightless" environment showed that the patient's body needed to be restrained or it would simply float away with the thrust.
Joseph Brimacombe, of the University of Queensland in Cairns, said: "The space shuttle definitely does not have the appropriate equipment for airway management by inexperienced personnel like astronauts."
The studies were reported in New Scientist magazine.