Chemiluminescent immunoassays performed in microtitre plates can be detected with a sensitive instant photoplate. An apparatus was constructed for this purpose making use of whole polystyrene microtitre plates plates possible. One of the advantages of immunoassays using enzyme-enhanced chemiluminescence is the possibility for developing homogeneous immunoassays. An example is described for a solid-phase immunoassay for 17 beta-testosterone making use of non-specific energy transfer in combination with photoplate detection. A testosterone-peroxidase conjugate was used as label. Quantification was performed using image-analysis techniques. The assay was also performed with colorimetric substrates for comparison.