Medial and lateral knee menisci were obtained from 20-week-old pigs, dissected into three zones of equal width, and analyzed for collagen and glycosaminoglycan content and for types of glycosaminoglycan and proteoglycan. The thin inner zones contained about 76% collagen and 8% glycosaminoglycan (by dry weight) and the outer zones, 93% collagen and 2% glycosaminoglycan. The most abundant glycosaminoglycan in all zones was chondroitin sulphate, accounting for about 80% of total glycosaminoglycan in the inner zones and 50-56% in the outer zones. Dermatan sulphate was the second most abundant glycosaminoglycan, present relative to chondroitin sulphate in a ratio of about 1:5-6 in the inner zones and 1:1.5 in the outer zones. Hyaluronic acid accounted for 4-5% of total glycosaminoglycan content in the inner zones and 10% in the outer zones. All compositional parameters for the middle zones were between those for the inner and outer zones. There were no statistically significant differences in composition between medial and lateral menisci. Proteoglycans were extracted and separated into two groups (large and small proteoglycans) by gel chromatography and were further characterized by gel electrophoresis. The large proteoglycans stained with use of monoclonal antibodies to chondroitin sulphate and keratan sulphate. Biglycan and decorin, two related dermatan sulphate proteoglycans, were identified in the small proteoglycan pool by their behaviour on gel electrophoresis and by immunostaining with specific antibodies. In the middle and inner zones, biglycan predominated. The observed lower electophoretic mobilities of dermatan sulphate proteoglycans from the inner zone compared with those from the outer zone were explained by the discovery of longer dermatan sulphate chains on the former. Collectively, these results show that the extracellular matrix of knee meniscus varies continuously across its width in a manner consistent with increased compressive loading on the thinner, inside aspect of the structure.