  We present a theoretical study of CS line profiles in archetypal hot cores.
We provide estimates of line fluxes from the CS(1-0) to the CS(15-14)
transitions and present the temporal variation of these fluxes. We find that
\textit{i)} the CS(1-0) transition is a better tracer of the Envelope of the
hot core whereas the higher-J CS lines trace the ultra-compact core;
\textit{ii)} the peak temperature of the CS transitions is a good indicator of
the temperature inside the hot core; \textit{iii)} in the Envelope, the older
the hot core the stronger the self-absorption of CS; \textit{iv)} the
fractional abundance of CS is highest in the innermost parts of the
ultra-compact core, confirming the CS molecule as one of the best tracers of
very dense gas.
