Editor, I read the recent study on “EPR as a tool for the evaluation of novel lyophilized blood products as absorbents for chemical gas masks” with a great interest.[1] Ivanov et al. concluded that “EPR can play a role in the evaluation of material for gas masks.”[1] I agree that the EPR is a good technique. However, I would like to note that there are some concerns on this technique. Jeschke and Polyhach noted that “The sensitivity of the technique and the reliability of the measured distance distribution depend on careful optimization of the experimental conditions and procedures for data analysis.”[2] Despite a good EPR, the error can still be at 0.1 nm.[3]