In response to the letter, "A better way to His-tag,"[1] I feel obliged to clear up any possible misunderstandings and allay the concerns of protein researchers currently using or planning to use Ni-NTA for purification of His-tagged proteins. The correspondent states: "These problems occurred due to the fact that Ni-NTA resin can nonspecifically oxidize protein side chains." This statement is not referenced, and to our knowledge, such a phenomenon has never been described in the scientific literature. The referenced article from Amersham Biosciences' Life Sciences News, which compares the properties of His-tagged protein constructs purified using either Ni-NTA or conventional chromatography, postulates that in some cases oxidation was responsible for unusual protein behavior, but offers no concrete proof.