E.U. laws on laying hens welfare imposed the conversion of housing systems from conventional to alternative ones, hence the necessity to study the influence on eggs production. Qualitatively, we monitored the alterations in eggs content for heavy metals and the incidence of any internal defects, due to system switching. 500 Lohmann Brown hens were used as biological material, randomly allocated in two groups: C group-conventional cages (250 hens), N group-newly improved cages (250 hens), while layer diet was unique. 100 eggs produced during the 28th week of fowl life (laying peak) were sampled from each group. Yolks and albumens were submitted to atomic absorption spectrometry to assess heavy metals. Pb was below detection limit (0.012 ppm). For other metals, there were found slightly higher levels in the yolks produced in the conventional system: Cd from 0.018 ppm (N group) to 0.021 ppm (C group); Cu from 2.553 ppm in improved cages vs. 2.617 ppm in conventional ones. Zn levels were quite similar in both systems, 5.346-5.367 ppm. Lower levels of heavy metals were also found in albumens, compared to yolks. All levels did not exceed the toxicity limits for humans. As internal defects, more blood and meat spots occurred in the eggs laid in C group, where fowl density was higher.