  Let $S$ be a set of $n$ red and $n$ blue points in general position in
$\mathbb{R}^3$. Let $\tau$ be a tetrahedra with vertices on $S$. We say that
$\tau$ is \emph{empty} if it does not contain any point of $S$ in its interior.
We say that $\tau$ is \emph{balanced} if it contains two blue vertices and two
red vertices. In this paper we show that $S$ spans $\Omega(n^{5/2})$ empty
balanced tetrahedra.
