Bethlehem police say when they responded to an alarm at Ralph and Shirley Lindgren's home on East Wall Street just after midnight, they ran into the couple's son, Michael.
The 51-year-old man was reportedly covered in blood.
Police say he told officers he "had to kill them".
When police went inside, they found the couple beaten unconscious, but alive.
Both are in critical condition with severe head injuries.
Michael Lindgren will be arraigned Monday on two counts of attempted homicide and other charges.