  The study of molecules and their chemistry in star-forming regions is
fundamental to understand the physical process occurring in such regions. The
HCN and HNC J=1-0 emissions were used to derive their integrated line
intensities (I), to probe a relation recently appeared in the literature
between the kinetic temperatures (T$_{K}$) and the isomeric (I) ratio, and to
obtain the isomers abundances (X) in 55 high-mass star-forming regions. These
last ones are classified, according to the evolutive stage, as infrared dark
clouds, high-mass protostellar objects, hot molecular cores, and ultracompact
HII regions. It is inferred that the T$_{K}$ obtained from the isomeric
integrated intensity ratio (I$^{HCN/HNC}$) are underestimated, and hence we
suggest that this relation cannot be employed as an universal thermometer in
the interstellar medium. The isomers abundances show a behavior that can be
explained from the chemistry occurring as the temperature and the UV radiation
increase according to the evolutive stage. We found that the abundance ratio
(X$^{HCN/HNC}$) hardly could be used as a chemical clock, and we suggest that
it can be approximated by I$^{HCN/HNC}$. This work is part of an on-going study
of multiple molecules that stand in the sample of analyzed regions which
intends to contribute in the chemical knowledge of high-mass star formation.
