Context :

Aims : The recent introduction of high-resolution/large spectral-range spectrographs has provided the opportunity to investigate the chemical composition of classical Cepheids in detail .
This paper focusses on new abundance determinations for iron and 6 light metals ( O , Na , Mg , Al , Si , Ca ) in 30 Galactic Cepheids .
We also give a new estimate of the Galactic radial abundance gradient .

Methods : The stellar effective temperatures were determined using the method of line depth ratios , and the surface gravity and the microturbulent velocity v _ { t } by imposing the ionization balance between Fe I and Fe II with the help of curves of growth .
Abundances were calculated with classical LTE atmosphere models .

Results : Abundances were obtained with RMS accuracies of about 0.05-0.10 dex for Fe , and 0.05-0.20 dex for the other elements .
Cepheids in our sample have solar-like abundances , and current measurements agree quite well with previous determinations .
We computed “ single zone ” Galactic radial abundance gradients for the 8-12 kpc region and found a slope for iron of -0.061 dex kpc ^ { -1 } .

Conclusions :