Many methods for the quantitative assessment of immunoglobulins have been described. Two of them are currently of the most value and of comparable accuracy: (1) radial immunodiffusion (RID) and (2) nephelometry. When patient load is relatively low, RID will probably remain the method of choice. However, with a high patient load and if nephelometer is already available, nephelometry is useful. Radial immunodiffusion has a constant coefficient of variation which, under optimal conditions , may be less than 10% except at extremely low concentrations. The limit of accurate protein measurements, using low concentrations of antisera, is about 10 mg/liter (10 μg/ml). Techniques using limited diffusion are more accurate than those with timed diffusion. With normal sera, results can be obtained after 24 hr of diffusion but more time may be required for the assessment of very high or very low levels.