  The first detection of a $^{36}$S-bearing molecule in interstellar space is
reported. The $J$=$2-1$ and $3-2$ transitions of C$^{36}$S have been observed
toward eight Galactic molecular hot cores. From a comparison with other
optically thin isotopic species of CS, the abundance ratio of $^{34}$S/$^{36}$S
is 115$(\pm 17)$. This is smaller than the solar system ratio of 200 and
supports the idea that $^{36}$S is, unlike the other stable sulfur isotopes, a
purely secondary nucleus that is produced by s-process nucleosynthesis in
massive stars.
