Measurement of radial immunodiffusion plates with a scanning densitometer

Measurement of the diameters of the precipitation rings in radial immunodiffusion plates with a scanning densitometer is described. Data obtained by scanning were compared with a conventional visual method of measurement and although the differences were statistically significant, the differences were small and there was no basis for determining which method was a more accurate estimation of concentration. It was concluded that the scanning method, which uses equipment present in most clinical pathology laboratories, is an acceptable alternative method for measuring radial immunodiffusion.