The Voyager 1 and 2 flybys of Saturn revealed the presence of a variety of plasma waves associated with Saturn's magnetosphere1,2, some electrostatic in nature, others apparently electromagnetic. Possibly the most unambiguous identification of the latter in the low-frequency range (< 10 kHz) is of narrow-banded emissions observed over a 3-day period when Voyager 1 was outbound3. Persistent bands of emission near 5 kHz were seen from 19 to 58 Rs (where Rs is Saturn's radius = 60,330 km), and, as the plasma parameters varied widely along the trajectory over this range, it is difficult to envisage how these emissions could be anything but freely-propagating electromagnetic waves. Hitherto their source was unknown, but similar emissions have been observed within the magnetospheres of Jupiter4 and Earth5–7 and, based on our knowledge of the latter in particular, it is proposed here that the source of the saturnian narrow-band emissions lies in electrostatic upper-hybrid waves near the equatorial plane just beyond the orbit of the moon Rhea.