Exciplex fluorescence in a mixture of N-ethylcarbazole (ECZ) and dimethyl terephthalate (DMTP) doped in a PMMA polymer film, which appears as a result of photoinduced electron transfer from ECZ to DMTP, is quenched by an electric field as the concentration of the electron donor, i.e., ECZ, is increased. Even when the DMTP concentration is increased, the exciplex fluorescence is not quenched by an external electric field as long as the ECZ concentration is low. These concentration dependences indicate that a hole transport occurs very efficiently and that an electron transport does not occur in this photoinduced electron-transfer system. In fact, a photocurrent could be detected in a mixture of ECZ and DMTP in PMMA films only when the concentration of ECZ was high.