ra·di·o·la·bel 
(rā′dē-ō-lābəl)
(rā′dē-ō-lābəl)tr.v. ra·di·o·la·beled, ra·di·o·la·bel·ing, ra·di·o·la·bels or ra·di·o·la·belled or ra·di·o·la·bel·ling
To tag (a hormone, enzyme, or other substance) with a radioactive tracer.
n.
A radioactive isotope used as a tracer; a radiotracer.