  We obtain asymptotic formulas with remainder terms for the hyperbolic
summations $\sum_{mn\le x} f((m,n))$ and $\sum_{mn\le x} f([m,n])$, where $f$
belongs to certain classes of arithmetic functions, $(m,n)$ and $[m,n]$
denoting the gcd and lcm of the integers $m,n$. In particular, we investigate
the functions $f(n)=\tau(n), \log n, \omega(n)$ and $\Omega(n)$. We also define
a common generalization of the latter three functions, and prove a
corresponding result.
