In the original (1987) Robocop movie, they use Alex Murphy's body to make Robocop.
What organic body parts did he retain?
Alex Murphy is subject to a total replacement of his body.
Tyler: [while creating RoboCop] We were able to save the left arm.
Bob Morton: What? I thought we agreed on total body prosthesis. Now, lose the arm, okay?
Assuming Robocop 2 is a good indicator, he probably also kept some of the nervous structure attached to the spine.