  Though S0 galaxies are usually thought to be `red and dead', they often
demonstrate weak star formation organised in ring structures and located in
their outer disks. We try to clarify the nature of this phenomenon and its
difference from star formation in spiral galaxies. The moderate-luminosity
nearby S0 galaxy, UGC 4599, is studied here. By applying long-slit spectroscopy
at the Russian 6m telescope, we have measured stellar kinematics for the main
body of the galaxy and strong emission-line flux ratios in the ring. After
inspecting the gas excitation in the ring using line ratio diagrams and having
shown that it is ionized by young stars, we have determined the gas oxygen
abundance by using conventional strong-line calibration methods. We have
inspected the gas kinematics in the ring with Fabry-Perot interferometer data
obtained at the William Herschel Telescope. The pattern and properties of the
brightest star formation regions are studied with the tunable filter MaNGaL at
the 2.5m telescope of the Caucasian Mountain Observatory of the Sternberg
Astronomical Institute (CMO SAI MSU). The gas metallicity in the ring is
certainly subsolar, [O/H]$=-0.4 \pm 0.1$~dex, that is different from the
majority of the outer starforming rings in S0s studied by us which have
typically nearly solar metallicity. The total stellar component of the galaxy
which is old in the center is less massive than its extended gaseous disk. We
conclude that probably the ring and the outer disk of UGC~4599 are a result of
gas accretion from a cosmological filament.
