Both oximes and hydroxylamine (HYAM) are compounds with known oxidative capacity. We tested in vitro whether acetaldoxime (AAO), cyclohexanone oxime (CHO), methyl ethyl ketoxime (MEKO) or HYAM affect haemoglobin oxidation (into HbFe3+), formation of thiobarbituric acid reactive substances (TBARS), and glutathione (GT) depletion in human haemolysate, erythrocytes or blood. All these parameters are known to be related to oxidative stress. Glutathione S-transferase (GST) activity was measured as it may be affected by oxygen radicals. All three oximes caused a low degree of HbFe3+ accumulation in erythrocytes. This was higher in haemolysates indicating that membrane transport may be limiting or that protective mechanisms within erythrocytes are more effective. HbFe3+ accumulation was lower for the oximes than for HYAM. AAO and HYAM caused TBARS formation in blood. For HYAM this was expected as free radicals are known to be generated during HbFe3+ formation. Free radical generation by AAO and HYAM in erythrocytes was confirmed by the inhibition of GST. For the other two oximes (CHO and MEKO) some special effects were found. CHO did inhibit erythrocyte GST while it did not cause TBARS formation. MEKO was the least potent oxime as it caused no TBARS formation, little HbFe3+ accumulation and little GST inhibition in erythrocytes. However, GT depletion was more pronounced for MEKO than for the other oximes, indicating that glutathione conjugation occurs. TBARS formation, GT depletion and GST modulation caused by the oximes and HYAM were also tested in rat hepatocytes. However, no effects were found in hepatocytes. This suggests that a factor present in erythrocytes is necessary for free radical formation. Studies with proposed metabolites of the oximes (i.e. cyclohexanone, acetaldehyde or methylethyl ketone) and addition of rat liver preparations to the erythrocyte incubations with oximes, suggest that metabolism is not a limiting factor in erythrocyte toxicity.