Erythrocyte glutathione transferase (e-GST) is overexpressed in case of increased blood toxicity and its level correlates with the kidney disease progression. Thus, it represents a probe of kidney efficiency against circulating toxins. We measured the activity of e-GST in patients with transplant kidney from living and cadaver donors, correlated its level to biochemical parameters of kidney function, and measured the level of oxidized albumin as a probe of oxidative stress using a new simple procedure. Interestingly, the activity of e-GST in transplant patients from cadaver donors (N = 153) is very high (11.7 U/gHb) compared to healthy subjects (N = 80) ( 5.6 U/gHb). Lower values were observed in transplant patients with kidney from living donors (N = 16) (9.8 U/gHb). Except for steroids, no correlation has been found with the immunosuppressive therapies and routine clinical and laboratory parameters. Also serum oxidized albumin, which reveals oxidative stress, is significantly higher in transplant patients from cadaver donors (53%) compared to that from living donors (36%). Overall, these data indicate that most of transplant kidneys from cadavers lost part of the detoxifying power against circulating toxins and suffer a relevant oxidative stress compared to those coming from living donors. A case report suggests that e-GST could represent a very early marker of incipient graft rejection. In conclusion, e-GST may be used to check the decline or maintenance of the kidney detoxification competence during post-transplantation course.