Electric field-induced modulation of the near-field photoluminescence of thin films of the conjugated polymer MEH-PPV was measured. A voltage bias applied between the near-field probe and the substrate results in a highly spatially confined electric field. The near-field photoluminescence intensity decreases when the sample bias is positive with respect to the probe while the intensity increases when the sample bias is negative. The modulation of photoluminescence intensity provides a sensitive measure of changes in the local carrier density induced by the applied electric field. Experiments performed with a blocking layer indicate that carriers are generated by photoexcitation in the bulk of the polymer film. On the basis of the modulation results, we estimate the concentration of holes under optical and electrical excitation to be 10(17) cm(-3). The temporal response of the fluorescence upon the application of voltage is described in terms of the carrier mobility and electric field.