OH 231.8+4.2 is an archetypal pre-planetary nebulae (pPN). It's
a binary system surrounded by bipolar nebula. Some years ago the
authors extensively studied it and performed several VLBI
observations from which they obtained mas-resolution maps of the SiO
(7 mm) and H$_2$O (1.3 cm) maser emissions (see Desmurs et al., 2004).
H$_2$O masers were found to be distributed in two areas along the
symmetry axis of the nebulae oriented nearly north-south delineating
a bipolar outflow and their astrometric positions were accurately
measured. SiO masers, indicating the position of the Mira component
of the binary system, form a structure perpendicular to the axis of
the nebulae. The general picture of the source looked satisfactory,
except for the relative position of the two masers. Surprisingly,
SiO masers, were tentatively placed 250 mas away (370 AU) from the
apparent center of the outflow. Using the ALMA we observed the SiO
maser emission at 86 GHz and accurately derived the position of the
Mira component. Combining our previous VLBA data and our new ALMA
observations we are now able to give a more complete and detailed
description of the inner part of this amazing pPN.