MLOs of faba bean phyllody and stolbur diseases were detected by a simple sensitive indirect immunofluorescence technique. Antisera prepared against membrane fractions of diseased plants were used with both 40 ,urn-thick sections obtained with a freezing microtome and with 7 ,urn-thick sections prepared from aldehyde-fixed paraffin-embedded plant materials. The technique is highly sensitive, simple to practice and utilizes small quantities of reagents. Specific MLO labeling was obtained using antisera with low titers and containing high proportions of anti-plant antibodies. The ease of using sections from fresh plant material suggests the potential use of the technique for routine indexing and screening of MLO infections. Immunofluorescence on sections from paraffin-embedded plant tissues improved the visualization of labeled MLOs, factilitated the accessibility of antigens, reduced non-specific labeling and allowed more precise localization and interpretation of immunofluorescent reactions. ZusammenfassungIn situ-Nachweis von Mycoplasrna-ahnlichen Organismen (MLOs)-Erreger von Stolbur bei Nachtschattengewachsen und Phyllodie bei Feldbohnen -durch indirekte Immunfluoreszenz