A high pressure mercury lamp with an extremely high mercury vapor pressure and extremely high tube wall load in which the arc during operation is advantageously stabilized is achieved in a high pressure mercury lamp having a discharge vessel of fused silica glass which contains a pair of opposed tungsten electrodes, mercury in an amount at least equal to 0.16 mg/mm.sup.3 and a rare gas, and in which the discharge tube has a tube wall load at least equal to 0.8 W/mm.sup.2, by at least one metal halide with a metal having an ionization potential that is at most 0.87 times as high as the mercury ionization potential being added to the discharge tube in a range of from 2.times.10.sup.-4 to 7.times.10.sup.-2 .mu.mole/mm.sup.3.