  Non-canonical scaling of the form $\rho_{x} \propto \rho_{m} a^{\xi}$, where
$\rho_{x}$ and $\rho_{m}$ are the energy densities of dark energy and dark
matter, respectively, provides a natural way to address the coincidence problem
-why the two densities are comparable today. This non-canonical scaling is
achieved by a suitable interaction between the dark components. We study the
observational constraints imposed on such models from the cosmic microwave
background (CMB) anisotropy spectrum. Using the recent WMAP results for the
location of the CMB peaks, we determine the admissible parameter space and find
that interacting models are well consistent with current observational bounds.
