Recent measurements of abundances in I Zw 18 compared to our applied composition (i.e. SMC composition scaled down by ten; shown by a red line with crosses). Carbon, nitrogen, oxygen, silicon and iron abundances are given relative to solar (Asplund et al. 2009): [X/H] = log(X/H)−log(X/H)_⊙. L13: first column of Table 7 in Lebouteiller et al. (2013). L13-HII: last column of the same table, composition of the HII regions. L04 and A03: data of previous measurements, taken from Lecavelier des Etangs et al. (2004) and Aloisi et al. (2003), respectively. 0.02 Z_⊙: solar abundances of Asplund et al. (2009) scaled down by a factor of 50.