The metallointercalator Rh(phi)(2)DMB(3+) (phi, 9,10-phenanthrenequinone diimine; DMB, 4,4’-dimethyl-2,2’-bipyridine) catalyzed the repair of a thymine dimer incorporated site-specifically in a 16-base pair DNA duplex by means of visible light, This repair could be accomplished with rhodium noncovalently bound to the duplex and at long range (16 to 26 angstroms), with the rhodium intercalator tethered to either end of the duplex assembly, This long-range repair was mediated by the DNA helix, Repair efficiency did not decrease with increasing distance between intercalated rhodium and the thymine dimer, but it diminished with disruption of the intervening pi-stack.