  For $n\geq 3$, we study the existence and asymptotic properties of the
fundamental solution for elliptic operators in nondivergence form, ${\mathcal
L}(x,\partial_x)=a_{ij}(x)\partial_i\partial_j+b_k(x)\partial_k$, where the
$a_{ij}$ have modulus of continuity $\omega(r)$ satisfying the square-Dini
condition and the $b_k$ are allowed mild singularities of order
$r^{-1}\omega(r)$. A singular integral is introduced that controls the
existence of the fundamental solution. We give examples that show the singular
drift $b_k\partial_k$ may act as a perturbation that does not dramatically
change the fundamental solution of ${\mathcal L}^o=a_{ij}\partial_i\partial_j$,
or it could change an operator ${\mathcal L}^o$ that does not have a
fundamental solution to one that does.
