Immunoturbidimetry and immunonephelometry are widely used immunoassays, especially popular in human clinical biochemistry for the determination of specific proteins. With the correct balance of antigen and antibody, the formation of antigen-antibody complexes can be followed in a spectrophotometer as flocculation occurs and light scattering increases. The light-scattering can be measured as absorbance increase (immunoturbidimetry) or scattered light increase (immunonephelometry). The methods are fast (just a few minutes) and easy to automate, but it is only suitable for protein concentrations above 5 mg/liter.