  We present an analysis of high-resolution spectra of three
core-helium-burning "clump" stars and two first ascent giants in the open
cluster IC 4651. Atmospheric parameters (T_eff, log_g, v_t, and [Fe/H]) were
determined in our previous study by Carretta et al. (2004). In this study we
present abundances of C, N, O and up to 24 other chemical elements. Abundances
of carbon were derived using the C_2 Swan (0,1) band head at 5635.5 A. The
wavelength interval 7980-8130 A, with strong CN features, was analysed in order
to determine nitrogen abundances and 12^C/13^C isotope ratios. The oxygen
abundances were determined from the [O i] line at 6300 A. Compared with the Sun
and other dwarf stars of the Galactic disk, mean abundances in the investigated
clump stars suggest that carbon is depleted by about 0.3 dex, nitrogen is
overabundant by about 0.2 dex and oxygen is close to solar. This has the effect
of lowering the mean C/N ratio to 1.36 +- 0.11. The mean 12^C/13^C ratios are
lowered to 16 +- 2. Other investigated chemical elements have abundance ratios
close to the solar ones.
