['To examine, by immunohistochemistry, the localization and distribution of human collagenase-3 in normal, osteoarthritis (OA), and rheumatoid arthritis (RA) cartilage, and to investigate the effects of interleukin-1beta (IL-1beta) and transforming growth factor beta (TGFbeta) on the synthesis and distribution of collagenase-3.', 'Human cartilage specimens were obtained from tibial plateaus. In the first series of experiments, the OA specimens were excised from fibrillated and nonfibrillated areas of cartilage, and RA specimens were excised from lesional areas, including the cartilage-pannus junction when present. In the second series, full strips of cartilage were processed for culture in the presence or absence of IL-1beta (100 units/ml) or TGFbeta (150 ng/ml). Each specimen was processed for immunohistochemical analysis using a collagenase-3 monoclonal antibody.', 'The number of cells that stained for collagenase-3 in normal cartilage was very low (approximately 3%). In OA cartilage, the percentage increased dramatically, and no difference was found between fibrillated and nonfibrillated areas. A statistically significant increase in the percentage of cells staining for collagenase-3 was found in the deep layer compared with the superficial layer. This finding was noted in both the fibrillated areas (mean +/- SEM 58.4 +/- 1.6% and 40.1 +/- 3.9%, respectively; P < 0.007) and the nonfibrillated areas (55.4 +/- 3.2% and 43.2 +/- 2.7%; P < 0.01). Similarly, RA cartilage showed a statistically significant (P < 0.001) increase in the level of chondrocytes staining positive for collagenase-3 in the deep layers (46.4 +/- 4.1%) compared with the superficial layers (26.2 +/- 3.4%). In these RA specimens, the numbers of positively staining chondrocytes were similar both close to and at a distance from the pannus junction. Both IL-1beta and TGFbeta increased the number of chondrocytes producing collagenase-3. Interestingly, in normal specimens, TGFbeta had a predominant effect in the deep layers, while IL-1beta had a greater effect on the superficial layers.'] Is collagenase-3 ( matrix metalloprotease 13 ) preferentially localized in the deep layer of human arthritic cartilage in situ : in vitro mimicking effect by transforming growth factor beta?