The relationship of lysosomes, multivesicular bodies (MVB's), and tubulovesicular structures (TVS) of the chondrocyte from rat epiphyseal cartilage was studied with ultrastructural cytochemical methods for the localization of acid phosphatase, endocytosed horseradish peroxidase (HRP), and sulfated and vicinal glycol-containing complex carbohydrates. Lysosomes contained intense uniformly distributed acid phosphatase activity. MVB's with an abundant fibrogranular matrix (dark) demonstrated strong acid phosphatase staining, whereas MVB's with a sparse matrix (light) stained less intensely or lacked staining. TVS associated with Golgi elements were acid phosphatase positive, whereas other TVS lacked staining. Incubation of viable chondrocytes with HRP resulted in macroendocytic (phagocytic) and microendocytic (pinocytic) engulfment with significant incorporatin into MVB's and some TVS as demonstrated by diaminobenzidine staining. Both acid phosphatase-positive and HRP-containing TVS appeared to contact and fuse with MVB's. High iron diamine (HID) failed to stain sulfated glycoconjugates in lysosomes and TVS in contrast to heavily stained secretory granules. MVB's stained weakly or not at all with the HID method. Periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP) strongly stained vicinal glycol-containing glycoconjugates in lysosomes. MVB's, TVS, and microendocytic caveolae. The PA-TCH-SP reactivity of the limiting membranes of MVB's, lysosomes, and TVS was much stronger that the reactivity associated with the plasmalemma and secretory granule membranes. These studies indicate chondrocyte lysosomes, MVB's and TVS represent part of a complex system engaged in processing phagocytosed material. This endocytic activity as measured by HRP incorporation was greatest in chondrocytes of the hypertrophic zone and may be related to matrix modification necessary for calcification and/or matrix reutilization.