The lipid peroxidation (tbars) levels of fertile cyst liquids (0.84+/-0.14, 0.9+/-0.12 micromol/L) for sheep liver and lung, respectively, were higher than infertile cyst liquids (0.29+/-0.07, 0.20+/-0.06 micromol/L) for sheep liver and lung (p < 0.05). There were no significant differences between fertile cyst membranes (0.71+/-0.12, 0.74+/-0.27 nmol/mg wet tissue protein for liver and lung, respectively) and infertile cyst membranes (0.37+/-0.11, 0.39+/-0.15 nmol/mg wet tissue protein) in terms of tbars levels (p > 0.05). The lipid peroxidation levels determined for protoscoleces (1.99+/-0.45, 2.07+/-0.20 nmol/mg wet tissue protein for sheep liver and lung, respectively) were significantly higher than those of fertile cyst membranes (p < 0.05) and than those of infertile cyst membranes (p < 0.01). NO levels of cattle fertile hydatid liquids (liver nitrite; 2.07+/-0.73 nmol/L, liver nitrate; 4.01+/-1.15 micromol/L, lung nitrite; 2.44+/-0.70 umol/L, lung nitrate; 0.87+/-0.30 micromol/L) were significantly higher compared to cattle infertile hydatid liquids (liver nitrite; 0.66+/-0.29 micromol/L, liver nitrate; 1.10+/-0.41 umol/L, lung nitrite; 0.55+/-0.15 micromol/L, lung nitrate; 0.54+/-0.16 micromol/L) (p < 0.05).