1. Tethered crickets (Gryllus campestris) walking on an air-suspended ball exhibit a spontaneous response to thee-vector of polarized light presented from above. In this study we determined the spectral sensitivity of polarization vision by finding the threshold light intensities for eliciting thise-vector response at different wavelengths. 2. The behaviorally determined spectral sensitivity was compared with the spectral sensitivity of the three spectral receptor types of the cricket eye (UV, blue, green) as measured electrophysiologically. The best match was obtained with the blue-receptor. This supports the thesis that polarization vision in crickets is mediated by the anatomically and physiologically specialized dorsal rim area of the eye. This part of the eye contains only blue-receptors, whereas other eye regions consist of UV- and green-receptors. 3. The absolute sensitivity of the cricket'se-vector detection system is very high. The threshold irradiance (at 50% of the maximal response) at 433 nmis 2.5×107 quanta cm−2 s−1, which is even lower than the effective quantum flux (range 380–500 nm) under the clear, moonless night sky.