Photonic-crystal fiber (PCF) is shown to substantially increase the guided-wave luminescent response from molecules excited through two-photon absorption (TPA) by femtosecond near-infrared laser pulses. With only a few nanoliters of TPA-excited molecules filling airholes in a specifically designed PCF, the guided-wave two-photon-excited luminescence (TPL) signal is enhanced by more than 2 orders of magnitude relative to the maximum TPL signal attainable from a cell with the same dye excited and collected by the same PCF. Biophotonic implications of this waveguide TPL-response enhancement include fiber-format solutions for online monitoring of drug delivery and drug activation, interrogation of neural activity, biosensing, endoscopy, and locally controlled singlet oxygen generation in photodynamic therapy.