The Hall effect in the organic metal alpha-(ET)2TlHg(SCN)4 has been st
udied over the temperature range 1.8-20 K. The field was directed alon
g various crystallographic axes in the conducting plane of the crystal
. The Hall constant is positive over the entire temperature range. It
increases sharply near 10 K. This behavior is interpreted as a metal-m
etal phase transition at 10 K.