Objective— To investigate the interrelation between plasma γ-glutamyltransferase (GGT) activity, cysteinyl-glycine (Cys-Gly) (ie, a thiol originating from GGT-mediated cleavage of glutathione), and oxidized low-density lipoprotein (oxLDL) with regard to myocardial infarction (MI) risk in a prospective study. Methods and Results— Incident cases of MI were identified among European Prospective Investigation into Cancer and Nutrition (EPIC)-Potsdam participants without prior MI during 6.0 years of follow-up. Baseline levels of Cys-Gly and oxLDL and GGT activity in plasma were measured in a case-cohort study comprising 837 subjects without incident MI and 116 subjects with incident MI. The relation of GGT, Cys-Gly and oxLDL to MI risk was assessed using Cox proportional hazards regression analysis. After adjustment for established risk factors, hazard ratios associated with a 1-SD unit increase in the log-transformed biomarker were 1.63 (95% CI, 1.30 to 2.05) for GGT, 1.36 (95% CI, 1.07 to 1.72) for Cys-Gly, and 1.37 (95% CI, 1.00 to 1.86) for oxLDL. Cys-Gly and oxLDL accounted for 2.3% of the relation between GGT and MI risk. Conclusion— The positive association between GGT activity and MI risk appears to be independent of circulating Cys-Gly and oxLDL levels. With Cys-Gly, we found a potential new predictor of MI risk whose impact needs to be further elucidated.