Context :

Aims : We aim to derive the chemical pattern of the young clusters 25 Orionis and \lambda Orionis through homogeneous and accurate measurements of elemental abundances .

Methods : We present flames/uves observations of a sample of 14 K-type targets in the 25 Ori and \lambda Ori clusters ; we measure their radial velocities , in order to confirm cluster membership .
We derive stellar parameters and abundances of Fe , Na , Al , Si , Ca , Ti , and Ni using the code MOOG .

Results : All the 25 Ori stars are confirmed cluster members without evidence of binarity ; in \lambda Ori we identify one non-member and one candidate single-lined binary star .
We find an average metallicity [ Fe/H ] = -0.05 \pm 0.05 for 25 Ori , where the error is the 1 \sigma standard deviation from the average . \lambda Ori members have a mean iron abundance value of 0.01 \pm 0.01 .
The other elements show close-to-solar ratios and no star-to-star dispersion .

Conclusions : Our results , along with previous metallicity determinations in the Orion complex , evidence a small but detectable dispersion in the [ Fe/H ] distribution of the complex .
This appears to be compatible with large-scale star formation episodes and initial non-uniformity in the pre-cloud medium .
We show that , as expected , the abundance distribution of star forming regions is consistent with the chemical pattern of the Galactic thin disk .