  We determine the integral extension groups
$Ext^1({\Delta}(h),{\Delta}(h(k)))$ and $Ext^k({\Delta}(h),{\Delta}(h(k)))$,
where ${\Delta}(h),{\Delta}(h(k))$ are the Weyl modules of the general linear
group $GL_n$ corresponding to the hook partitions $h=(a,1^b)$,
$h(k)=(a+k,1^{b-k})$.
