Cytokines are important mediators in inflammation, and play a key role in inflammation induced by Gram-negative bacteria. Cytokines are released into serum during different pathological conditions, such as meningococcal disease, and the cytokine levels in serum seem to correlate with fatal outcome of septic shock (1-3). Consequently, detection of cytokines in serum samples from patients with pathological diseases may be of prognostic and clinical value. Cytokines can be detected using bioassays and immunoassays, and this chapter focuses on description of bioassays for detection of tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1), and IL-6 in serum samples.