  We determined the chemical composition of a large sample of weak G band stars
-- a rare class of G and K giants of intermediate mass with unusual abundances
of C, N, and Li. We have observed 24 weak G band stars with the 2.7 m Harlan J.
Smith Telescope at the McDonald Observatory and derived spectroscopic
abundances for C, N, O, and Li, as well as for selected elements from Na - Eu.
The results show that the atmospheres of weak G band stars are highly
contaminated with CN-cycle products. The C underabundance is about a factor of
20 larger than for normal giants and the $^{12}$C/$^{13}$C ratio approaches the
CN-cycle equilibrium value. In addition to the striking CN-cycle signature the
strong N overabundance may indicate the presence of partially ON-cycled
material in the atmospheres of the weak G band stars. The exact mechanism
responsible for the transport of the elements to the surface has yet to be
identified but could be induced by rapid rotation of the main sequence
progenitors of the stars. The unusually high Li abundances in some of the stars
are an indicator for Li production by the Cameron-Fowler mechanism. A
quantitative prediction of a weak G band star's Li abundance is complicated by
the strong temperature sensitivity of the mechanism and its participants. In
addition to the unusual abundances of CN-cycle elements and Li we find an
overabundance of Na that is in accordance with the NeNa chain running in
parallel with the CN-cycle. Apart from these peculiarities the element
abundances in a weak G band star's atmosphere are consistent with those of
normal giants.
