The results demonstrated that both antibodies rendered several cross-reactive bands when probed on Western blots. The most obvious cross-reaction of the CYP2 antibody was with a strongly expressed protein of size ≈57 kDa, pI 4.5–4.6, whereas the CYP4 antibody cross-reacted with a protein of size ≈55 kDa, pI 5.6. However, expression of cross-reacting proteins did not change as a result of the exposures, and resulted only in small and insignificant fluctuations in total CYP content. As a contrast, silver-stained 2DE gels showed that several microsomal proteins were affected in individuals exposed to diallylphthalate as well as crude oil, with and without a spike of alkylphenols and PAHs. Mass spectrometry based analyses of excised, trypsin-digested spots did so far not decipher the identities of the proteins affected by the exposures, nor of those cross-reacting with CYP2 and CYP4 antibodies.