Based on high-resolution, high signal-to-noise ratio spectra, we have derived accurate metallicities for 15 extrasolar planet host stars, as well as differential abundances for 16 other elements. The companions of three stars, HD 29587, HD 98230, and possibly HD 190228, have been shown to have masses in the brown dwarf regime and give an average value of the metallicities [Fe/H] = -0.44 ± 0.17. If we exclude these three stars, the rest of the sample stars are metal-rich relative to the Sun, covering the range from -0.12 to 0.41, with an average [Fe/H] value of 0.16 ± 0.17. The stars with planets show a slight overabundance pattern for [Na/Fe], [Mg/Fe], [Al/Fe], and [Sc/Fe]. On the other hand, [C/Fe], [O/Fe], [Si/Fe], [Ca/Fe], [Ti/Fe], [V/Fe], [Cr/Fe], [Ni/Fe], and [Ba/Fe] are approximately solar in the sample. The stars with planets also show underabundances for [K/Fe] and slight overabundances for [Mn/Fe], but stars with brown dwarfs show a contrary trend for these two elements. An interesting result is that sulfur displays enhanced values of [S/Fe], ranging from 0.04 to 0.40 through the sample. These results are used to investigate the connection between giant planets and high metallicity and to probe the influence of this process on the other elements.
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