  An accurate analytic approximation of the transfer function for the power
spectra of primordial density perturbations in mixed dark matter models is
presented. The fitting formula in a matter-dominated Universe
($\Omega_0=\Omega_M=1$) is a function of wavenumber $k$, redshift $z$ and four
cosmological parameters: the density of massive neutrinos, $\Omega_{\nu}$, the
number of massive neutrino species, $N_{\nu}$, the baryon density, $\Omega_{b}$
and the dimensionless Hubble constant, $h$. Our formula is accurate in a broad
range of parameters: $k\le 100 h/Mpc$, $z\le 30$, $\Omega_{\nu}\le 0.5$,
$N_{\nu}\le 3$, $\Omega_{b}\le 0.3$, $0.3\le h\le 0.7$. The deviation of the
variance of density fluctuations calculated with our formula from numerical
results obtained with CMBfast is less than 6% for the entire range of
parameters. It increases with $\Omega_bh^{2}$ and is less than $\le 3%$ for
$\Omega_bh^{2}\le 0.05$.
  The performance of the analytic approximation of MDM power spectra proposed
here is compared with other approximations found in the literature. Our
approximation turns out to be closest to numerical results in the parameter
space considered here.
