A mercury‐vapor filled proportional counter is described. Its behavior as a &ggr; counter is investigated. The resolution is fair (7.5% energy spread at 60 kev); however, the various mercury x‐ray fluorescence yields and absorption cross sections combine to make the output spectrum of the counter complex and difficult to interpret. It is found that the output pulses are slow, rising in about 30 &mgr;sec, though this can be reduced to about 8 &mgr;sec by addition of CO2to the filling.