  The effect of neutrino cooling of possible primary regions filled by the hot
matter is discussed. Such regions could contain the primordial density
inhomogeneities of different origin and survive up to modern epoch. We show
that the final temperature of such region is $\sim 10\, {\rm keV}$ provided
that the initial temperature is within the interval $10\, {\rm keV} ... 100\,
{\rm MeV}$. The cooling is realized due to the nuclear reactions containing
$n-p$ transition. The lower limit $10\, {\rm keV}$ is accounted for by
suppression of the reactions rates because of threshold effect and $n$,
$e^{\pm}$ density diminishment.
