The classic Sherman-Lauricella integral equation and an integral equation d
ue to Muskhelishvili for the interior stress problem are modified. The modi
fied formulations differ from the classic ones in several respects: Both mo
difications are based on uniqueness conditions with clear physical interpre
tations and, more importantly, they do not require the arbitrary placement
of a paint inside the computational domain. Furthermore, in the modified Mu
skhelishvili equation the unknown quantity, which is solved for, is simply
related to the stress. In Muskhelishvili's origional formulation the unknow
n quantity is related to the displacement. Numerical examples demonstrate t
he greater stability of the modified schemes. [S0021-8936(00)01304-0].