We present the first metallicity distribution functions of the old field populations in the Magellanic Clouds .
Our metallicities are based on the Fourier decomposition of Type ab RR Lyrae light curves from the Optical Gravitational Lensing Experiment ( OGLE-III ) .
 On the metallicity scale of Zinn & West ; we find a mean metallicity of \mathrm { [ Fe / H ] } = -1.50 \pm 0.24 dex based on 16776 RR Lyrae stars in the Large Magellanic Cloud ( LMC ) .
For the Small Magellanic Cloud ( SMC ) we obtain -1.70 \pm 0.27 dex based on 1831 RR Lyrae stars .
These uncertainties represent the intrinsic spread in the population rather than the standard deviation of the mean . Our results are in good agreement with the few existing spectroscopic metallicity determinations for LMC RR Lyrae stars from the literature .
For both the LMC and the SMC the metallicity spread exceeds 1 dex in [ Fe/H ] .
 The distribution of metallicities in both Clouds is very uniform , and no significant metallicity gradient is detectable .
 We also do not find any pronounced populations of extremely metal-poor RR Lyrae candidates with metallicities well below -2 dex , although we need to caution that the photometric method used may overestimate the metallicities of metal-deficient stars .
Moreover , because of stellar evolutionary effects one does not expect to observe many RR Lyrae stars among very metal-poor horizontal branch stars. We suggest that the Magellanic Clouds experienced fairly rapid and efficient early enrichment involving pre-enriched gas as well as possibly gas infall , while metal loss through outflows does not seem to have played a significant role .
Moreover we suggest that the differences in the metallicities of the old population of LMC and SMC make an origin from a single , common progenitor unlikely , unless the separation happened very early on .