Doctors said the boys were in a critical, but stable condition.
Ahmad and Muhammad were born in June 2001 in a small town 800km (500 miles) south of the Egyptian capital and were transferred immediately to the University of Cairo Hospital.
The World Craniofacial Foundation of Dallas brought them to Texas in June 2002 and the surgical team studied their case for more than a year before last weekend's 24-hour operation to separate them.
The twins "continue to progress well and are coming out of their medically induced comas," said James Thomas, chief of critical care services at Children's Medical Centre in Dallas.
He said doctors had stopped administering the sedative that had been keeping Muhammad in a comatose state, but continued to give a low dosage to Ahmad because "he showed some involuntary twitching on his right side, which the surgeons and the medical team interpreted as seizures.
"This can be expected following neurosurgery and was quickly treated," Thomas said, adding: "None of the people involved in these boys' care think that this is of major importance, particularly since it was controlled so readily.
"So far, the boys show no signs of infection, and the preventive antibiotics they had been receiving were stopped as planned on Wednesday evening"
chief of critical care services at Children's Medical Centre, Dallas
"So far, the boys show no signs of infection, and the preventive antibiotics they had been receiving were stopped as planned on Wednesday evening," he said.
He said the attending medical team was "pleased with their improvement".
But he added a note of caution, saying: "It is worth acknowledging that other children engaged in similar struggles have not survived."
Success in Vietnam
Meanwhile, Vietnamese twins Le Thu Cuc and Le Thuy An were in a stable condition on Friday after their first night apart, but doctors warned that the 10-month-old girls still faced a difficult road to recovery.
The pair were separated on Thursday at the Central Paediatric Institute in Hanoi after an operation lasting about 10 hours.
"The children are in pretty stable condition. They were taken off respiratory machines this morning. An has a slight fever and we will keep watching her closely," said institute director Dr Nguyen Thanh Liem.
"Up until now, their situation is under control, however they face difficult times ahead. The children will be kept in our intensive care until they are really strong and healthy," added Liem, who headed the 30-strong surgical team.
The twins, who were joined at the chest and abdomen, each had their own heart and liver but their organs had been joined together. They had also shared intestines.