  We report observations of a new AM Herculis binary identified as the optical
counterpart of the X-ray source RX J1313.2-3259, detected during the ROSAT
All-Sky Survey (RASS). It has an orbital period of 251 min and is strongly
modulated at optical wavelengths. The long-term behavior is characterized by a
pronounced variation in X-rays between the RASS and two subsequent pointings
(decrease by a factor 40 in count rate) and by moderate changes in the optical
brightness (up to a factor 5). The X-ray spectrum is dominated by a soft
quasi-blackbody component, with a smaller contribution from thermal
bremsstrahlung. Measurements of high circular polarization confirm its
classification as a Polar with a magnetic field strength of 56 MG. The average
visual magnitude of RX J1313.2-3259 is V = 16 mag, for its distance we get 200
pc.
