  We consider equations of the form $(D_{(\rho)}u)(t)=-\lambda u(t)$, $t>0$,
where $\lambda >0$, $D_{(\rho)}$ is a distributed order derivative, that is the
Caputo-Dzhrbashyan fractional derivative of order $\alpha$, integrated in
$\alpha\in (0,1)$ with respect to a positive measure $\rho$. Such equations are
used for modeling anomalous, non-exponential relaxation processes. In this work
we study asymptotic behavior of solutions of the above equation, depending on
properties of the measure $\rho$.
