A proof is given of an abstract characterization of operators of the form $$\sum_{i,j=1}^{n} \, \frac{\partial}{\partial x_{i}} \left( a_{ij} \, \frac{\partial}{\partial x_{j}} \right) + \sum_{i=1}^{n} \, b_{i} \,\frac{\partial}{\partial x_{i}} + c \qquad \qquad (a_{ij} = a_{ji})$$ with $a_{ij} \in L^{\infty}(\Omega)$, $b_{i} \in L^{r}(\Omega)$$(r>2)$, $c \in L^{q}(\Omega)$$(q>1)$, $\Omega$ open set of $\mathrm{R}^{n}$, by particular continuous forms on $H_{0}^{1} \times (H_{0}^{1} \cap L^{p})$.