We have studied electric properties of carrier-injected deoxyribonucleic acid (DNA) molecules. First, a current (I-CA) through a single DNA molecule was measured by the two-probe dc method with varying a distance between a cathode and an anode (d(CA)). The I-CA-d(CA) curve showed that the current rapidly decreased with increasing d(CA) (I(CA)less than or similar to0.1 nA for d(CA)greater than or similar to6 nm) according to a hopping model. Next, we measured electric properties of DNA injected carriers by two methods; a field effect transistor (FET) arrangement and a chemical doping. In the FET arrangement, we set three electrodes on a single DNA molecule as source, drain, and gate electrodes with a source-drain distance (d(DS))similar to20 nm. When a voltage was applied to the gate, the source-drain current (I-DS) could be detected to be 0.5-2 nA. This showed that charge injection with the FET arrangement would yield a carrier transportation through DNA at least d(DS)similar to20 nm. In order to flow a current through DNA over a distance similar to100 mum, we synthesized the DNA-acceptor cross-linked derivatives (DACD). In the structure of DACD, DNA molecules, which were attached acceptor molecules at guanine sites specifically, were cross-linked by linker molecules. We can modulate the carrier concentration in DACD with changing a guanine-cytosine pair content (p(GC)) in a DNA double strand. We measured the current-voltage curves of DACD for various p(GC). The conductivity of DACD increased nonlinearly with an increase in p(GC). We explained this behavior using a percolation model, so that a two-dimensional conductive network would form in DACD. (C) 2003 American Institute of Physics.