Abstract: Apparatus for carrying out double or radial immunodiffusion analysis comprises a circular plate with an upstanding rim therearound. One face of the plate and the rim together form a trough within which a diffusion medium layer can be formed. A plurality of cylindrical walls project from the opposite face of the plate and define sample wells which open via respective apertures in the plate into the trough. Samples to be analysed are placed in the wells from where they diffuse into a said diffusion medium layer formed in the trough. External contamination is prevented by a cover which engages the rim to enclose the trough, and by a sealing film placed over the ends of the cylindrical walls remote from the plate to close off the wells.