Afferent lymph vessels entering the popliteal lymph nodes of sheep were infused with [3H]acetyl-labelled hyaluronan [HA; Mr of (0.85-1.2) x 10(5)] for up to 4 h at a rate of 17.4-23.1 micrograms/h. As much as 22.8 micrograms (99%) of infused [3H]HA was taken up by the node per h and degraded. During this interval it was observed that infused HA polymers of higher Mr were absorbed by the node to a greater degree than those of lower Mr. When proteoglycan monomer (PG; Mr 5 x 10(5); 400 micrograms of hexuronic acid/h) was infused concurrently with [3H]HA, the absolute amount of radioactivity appearing in efferent lymph (i.e. labelled material not absorbed by the node) increased, whereas the amount of labelled metabolites of low Mr was reduced considerably. During this period the Mr distribution of labelled HA in efferent outflow reverted to that of the infused material within 30-60 min. Our findings suggest that PG subunits and their chondroitin sulphate chains compete with HA for uptake into the peripheral lymph node of sheep. This indicates that PG, chondroitin sulphate and HA share the same pathway of elimination in this tissue, and is consistent with the view that the lymph node is involved in the metabolic turnover of normal intracellular matrix.