With standardized bacteriological methods, where direct microscopic examination took a very important place, 112 effusions from children (aged 1 to 6 years) with OME (minimum 2 months duration) were examined. It was demonstrated that acridine orange stain was superior to Gram stain in detecting bacteria, while Giemsa stain gave more information about the inflammatory cells involved. Purulent OME revealed most frequently bacteria (in total 92%), as well by direct microscopic examination (83%) as by culture (83%). Bacteria were found in the direct microscopic examination of 45% of the serous and 72% of the mucoid secretions. Cultures were positive in 45% of the serous and in 32% of the mucoid effusions. In the mucoid group, the sticky glue effusions had the lowest detection rate, especially when culturing (only 21% positive cultures). Polymorphonucleocytes were present in all purulent but also in all serous effusions, and in 76% of the mucoid effusions (57% of glue effusions). Lymphocytes often accompanied polymorphonucleocytes, especially in serous (45%) and seromucoid (47%) effusions. Mono-nuclear cells and macrophages were only rarely found.