Cholesteatoma epithelium, squamous epithelium not producing cholesteatoma, and granulation tissue specimens, obtained during radical ear surgery, were subjected to total LDH activity as well as isoenzyme analyses. The isoenzyme pattern of the patients’ serum had the normal marked emphasis on LDH1–3 fractions. The tissue specimens all showed a shift of emphasis towards the slowly mobile LDH4–5 fractions. In total LDH activity analysis actively growing granulation tissue was found to show the largest figures, even if the isoenzyme surface percentages were similar to those of epithelial tissues or non-active granula