An armed space engineer killed a co-worker he had taken hostage, then himself, in an attack last night at Nasa's Johnson Space Center.
Another hostage, a female co-worker, was found bound with duct tape, but unharmed, police said.
"Apparently there was some type of dispute between the suspect and the victim," Houston police chief Harold Hurtt said.
The incident occurred amid rising concerns about US gun violence following the Monday attack at Virginia Tech university in which a student killed 32 people in the worst shooting rampage in modern US history.
"As a result of the Virginia Tech shootings, we had reviewed our own (security) procedures here at the Johnson Space Center," center director Michael Coats told reporters.
"Of course, we never believed this could happen," he said.
Coats identified the shooter as Bill Phillips, who had worked at JSC for 12 years but was a contract worker employed by Pasadena, California-based Jacobs Engineering Group.
"Up until recently, he's been a good employee," he said.
The dead co-worker was David Beverly, an engineer employed by NASA, Coats said. Both men were said to be in their 50s.
The incident began about 1:40 pm (6.40pm Irish time) when, in the building where they worked, Phillips pulled out a gun and was heard firing at least two shots, police said.