Pyrogen tests are safety assays performed during the routine quality control of injectable products required by regulatory agencies. Currently, there are three available testing possibilities: 1) the Rabbit Pyrogen Test (RPT); 2) the Bacterial Endotoxin Test (BET); and 3) test systems using human whole-blood or monocytes, termed Monocyte Activation Test (MAT). Although BET is often considered as a replacement for the animal test, it is unable to detect pyrogens other than endotoxin. MAT is based on the human fever reaction and thus, most closely reflects the human response. The aim of this study was to conduct a parallel comparison of the RPT and MAT for hyperimmune sera (HS) batches analyzed during the routine of a quality control laboratory.MATwas performed in the same 43 batches of HS previously tested using RPT. The results showed thatMAT presented 100% sensitivity and approximately 85% specificity as compared to RPT, i.e., no false-negative results were obtained. Few suspicious samples,which were negative in the RPT after retesting, provided divergent positive results suggesting a lower limit of detection of MAT. MAT is thus able to detect contaminants in biological products such as HS batches.