Rat liver cathepsin D (EC 3.4.23.5) was purified using precipitation technique, ion exchange chromatography, molecular sieve chiomatography and isoelectric focusing. Rabbit anti-rat cathepsin D IgG was prepared and rat incisor teeth were cross-sectioned in a cryostat. These sections were incubated with FITC-conjugated anti-rat cathepsin D IgG. Marked fluorescence, indicating the localization of cathepsin D. could be seen over the odontoblast and predentin area. No specific fluorescence could be demonstrated in the pulp connective tissue proper nor in the dentin