We determine Saturn's radio rotation period using measurements made by the Planetary Radio Astronomy experiment onboard the Voyager spacecraft. The sidereal period deduced is 10 hr 39 min 24 sec ¿7 sec. The radio rotation period is presumably that of the planet's magnetic field. We propose a provisional Saturn longitude convention, and we provide equations to compute a longitude ephemeris and to transform between the proposed system and the (10 hr 14 min) system used for the Pioneer 11/Saturn encounter. In addition, we evaluate the degree of longitude smearing which could result over the long term from the merging of data sets organized in this system. Finally, no evidence of control of the radio emission by any of Saturn's satellites is found.