  Let $(R, \mathfrak{m})$ be a regular local ring of dimension $d \geq 2$. A
local monoidal transform of $R$ is a ring of the form $R_1=
R[\frac{\mathfrak{p}}{x}]_{\mathfrak{m}_1}$ where $x \in \mathfrak{p}$ is a
regular parameter, $\mathfrak{p}$ is a regular prime ideal of $R$ and $
\mathfrak{m}_1 $ is a maximal ideal of $ R[\frac{\mathfrak{p}}{x}] $ lying over
$ \mathfrak{m}. $ In this article we study some features of the rings $ S=
\cup_{n \geq 0}^{\infty} R_n $ obtained as infinite directed union of iterated
local monoidal transforms of $R$. In order to study when these rings are GCD
domains, we also provide results in the more general setting of directed unions
of GCD domains.
