Aims It is commonly known that stored blood and blood products are heated before transfusion to prevent hypothermia, which leads to increased di-(2-ethylhexyl) phthalate (DEHP) content leaching into the blood and blood products and thereby causes greater conversion of DEHP to mono (2-ethylhexyl) phthalate (MEHP). However, there has been no study in the literature reporting on the amount of toxic phthalates in blood following the erythrocyte suspension (ES) transfused via warming. In this study, we aimed to investigate the DEHP and MEHP content in blood following the heated ES transfusions administered by DEHP-containing and DEHP-free infusion sets. Methods The study included 30 patients that were randomly divided into two groups with 15 patients each: group I underwent ES transfusion via DEHP-containing infusion sets warmed with blood-fluid warmers, and group II underwent ES transfusion via DEHP-free infusion sets warmed with blood-fluid warmers. DEHP and MEHP levels were measured both before and after transfusion. Results DEHP-free infusion sets led to no increase in the phthalate content, whereas DEHP-containing infusion sets significantly increased the DEHP and MEHP, where the DEHP level increased almost four times (P = .001). Conclusion DEHP-containing products lead to toxicity. Therefore, using DEHP-free medical devices may prevent toxicity in patients undergoing ES transfusion.