Doping studies of PbTe and Pb0.96Eu0.04Te epitaxial layers grown by molecular beam epitaxy on BaF2 (111) substrates are presented. Bi is used for n-type doping and it is supplied in the form of Bi2Te3 during epitaxial growth. The electrical properties of the layers were investigated by Hall effect measurements for Bi doping levels ranging from 10(17) to the mid 10(17) cm(-3). We observe a unity doping efficiency for Bi concentrations up to 5 X 10(19) cm(-3), above which the doping coefficient slowly decreases. The maximum achievable carrier density was 4.4 x 10(20) cm(-3) for PbTe and about 1 X 10(20) cm(-3) for Pb0.96Eu0.04Te. At these high doping levels, the doping efficiency was still as high as 40%. For even higher Bi doping concentrations a rapid structural degradation of the layers occurs since then the total Bi content in the layers is already a few percent, i.e., a ternary Pb1-xBixTe ternary alloy is formed.