In inflammatory gingival diseases, cytokines have been demonstrated to play critical roles by coordinating the stimulation of immunological and connective tissue cells. The activities of these cells, degrading and remodeling extracellular matrices, constitute the major pathological and repair processes. Thus, elucidating cellular and molecular events occurring in inflamed connective tissues is crucial for the understanding and treatment of inflammation. In order to test a hypothesis that proinflammatory cytokines affect metabolism of major extracellular matrix molecules, we studied metabolism of proteoglycans (PGs) by human gingival fibroblasts (HGF) under the influence of interleukin‐4 (IL‐4) as a model of gingivitis. HGF in cell culture were metabolically radiolabeled using [³H]glucosamine and [³⁵S]sulfate in the presence or absence of IL‐4, and the labeled PGs were analyzed by chromatographic techniques. The incorporation of ³⁵S into PGs increased with IL‐4 both in media and cell layer. At 100 ng/ml of IL‐4, the increment of ³⁵S incorporation over control culture was 16–39% (p<0.001) in media and 12–35% (p=0.01) in cell layer. The ³⁵S‐labeled macromolecules were PGs containing heparan sulfate (HS) and chondroitin sulfate (CS) chains. From the molecular weight and glycosaminoglycan composition analyses, versican and jrelecan‐type and biglycan and decorin‐type were very likely to be the major PG constituents both in media and cell layer. IL‐4 stimulated synthesis of versican and jrelecan‐type more potently than biglycan and decorin‐type. With IL‐4 treatment, the ratio of CSPG/HSPG decreased in media and increased in cell layer. This ratio suggested that syndecan family HSPGs were also present in HGF. In conclusion, IL‐4 stimulated accumulation of CS/HSPGs in human gingival fibroblasts.