Abstract: Method for immunological analysis of a trace component(s) by labelling an antigen or antibody with a marker comprising causing an immune reaction using an antigen or antibody labelled with a spectral sensitizer as a marker, separating the labelled antigen or antibody from the resulting antigen-antibody reaction product, then bringing either the labelled antigen or antibody and the labelled antigen-antibody reaction product into contact with a silver halide, exposing the resulting system to light having a wavelength which the spectral sensitizer absorbs, developing the thus exposed silver halide and then measuring the resulting density.Trace components can thus be photochemically detected and the amount present quantitatively determined. The method provides high reproducibility and high sensitivity comparable to radioimmunoassay but without any risk of radiation exposure.