A primary screening of monoclonal antibodies (mAbs) prepared by hybridoma technology requires the testing of a large number of hybridoma culture supernatants within a short time. In addition, the intended application of the mAbs (e.g. ELISA, immunoblot, neutralization, histochemistry) have to be considered when selecting the optimal screening procedure. We have developed a rapid micromethod for the primary screening of mAbs which permits the selection of antibodies suitable for immunohistochemistry in a single step. This method combines the capacity of an assay performed in 96-well plates and the specificity of a microscopic immunohistochemical technique. The capacity of classical immunohistochemical methods working with glass slides is limited to tens of preparations, but the improved screening micromethod allows the processing of hundreds of culture supernatants in one single round of the assay. The suitability of this novel screening system was established by the selection of mAbs recognising Alzheimer's disease (AD)-neurofibrillary pathology in histological preparations and phosphoprotein pp32 in rat brain sections.