The innate immune system is equipped with pattern recognition receptors (PRRs) that detect foreign nucleic acids, triggering signaling pathways that drive pro-inflammatory and interferon responses. While these immune reactions are crucial for antiviral defense, they can also present significant challenges for RNA-based therapeutics, leading to immunogenicity, toxicity, and/or reduced efficacy. Therefore, evaluating the immunogenicity of therapeutic RNAs is essential. This chapter provides detailed protocols for assessing the immunostimulatory potency of exogenous RNA using peripheral blood mononuclear cells (PBMCs) or whole blood, two widely used models for studying innate immune activation. The methods outlined include PBMC isolation from human blood, stimulation with synthetic or in vitro-transcribed mRNA, and subsequent cytokine measurement using enzyme-linked immunosorbent assays (ELISA).