. . . . . . "Context. We present deep archival VLT/FORS1+UVES spectroscopic observations of the system of two blue compact dwarf (BCD) galaxies SBS 0335-052E and SBS 0335-052W. Aims. Our aim is to derive element abundances in different H\u00A0 ii\u00A0regions of this unique system of galaxies and to study spatial abundance variations. Methods. The electron temperature Te (O iii) in all H\u00A0 ii\u00A0regions, except for one, is derived from the [O\u00A0 iii]\u00A0 \u03BB4363/( \u03BB4959+ \u03BB5007) flux ratio. We determine ionic abundances of helium, nitrogen, oxygen, neon, sulfur, chlorine, argon and iron. The empirical relations for ionization correction factors are used to derive total abundances of these elements. Results. The oxygen abundance in the brighter eastern galaxy varies in the range 7.11 to\u00A07.32 in different H\u00A0 ii\u00A0regions supporting previous findings and suggesting the presence of oxygen abundance variations on spatial scales of ~1-2\u00A0kpc. Good seeing during FORS observations allowed us to extract spectra of four H\u00A0 ii\u00A0regions in SBS\u00A00335-052W. The oxygen abundance in the brightest region No.\u00A01 of SBS\u00A00335-052W is 7.22\u00A0 \u00B1 0.07, consistent with previous determinations. Three other H\u00A0 ii\u00A0regions are much more metal-poor with an unprecedently low oxygen abundance of 12\u00A0+\u00A0log\u00A0O/H\u00A0= 7.01\u00A0 \u00B1 0.07 (region\u00A0No.\u00A02), 6.98\u00A0 \u00B1 0.06 (region\u00A0No.\u00A03), and 6.86\u00A0 \u00B1 0.14 (region\u00A0No.\u00A04). These are the lowest oxygen abundances ever derived in emission-line galaxies, supporting earlier conclusions that SBS\u00A00335-052W is the lowest-metallicity emission-line galaxy known. Helium abundances derived for the brightest H\u00A0 ii\u00A0regions of both galaxies are mutually consistent. We derive weighted mean He mass fractions of 0.2485\u00A0 \u00B1 0.0012 and 0.2514\u00A0 \u00B1 0.0012 for two different sets of He\u00A0 i\u00A0emissivities. The ratios of neon and sulfur to oxygen abundance are similar to the respective ratios obtained for other emission-line galaxies. On the other hand, the chlorine-to-oxygen abundance ratio in SBS\u00A00335-052E is lower, while the argon-to-oxygen abundance ratio is higher than those in other low-metallicity galaxies. The Fe/O\u00A0abundance ratios in different regions of SBS\u00A00335-052E are among the highest for emission-line galaxies implying that iron is almost entirely not depleted onto dust grains despite dust being detected in this galaxy in earlier ISO and Spitzer observations. The N/O\u00A0abundance ratio in both galaxies is slightly higher than that derived for other BCDs with 12\u00A0+\u00A0log\u00A0O/H\u00A0<\u00A07.6. This implies that the N/O in extremely metal-deficient galaxies could increase with decreasing metallicity."@en . . "SBS 0335-052E+W: deep VLT/FORS+UVES spectroscopy of the pair of the lowest-metallicity blue compact dwarf galaxies"@en . . . . . "2009"^^ . . . "2009"^^ . "\u00A9 ESO, 2009" . . . . . . "aa11965-09" . . "ESO" .