Rabbit meniscal fibrochondrocytes were grown in vitro under culture conditions previously shown to foster growth of this cell type. Regardless of the culture regimen employed, the cells synthesized sulfated proteoglycans which could be differentiated by their solubility when dialyzed against water. The water soluble proteoglycans (WSPG) were monomeric in nature and could be separated into sub-types based on their hydrodynamic size when analyzed by gel-filtration chromatography. The water insoluble proteoglycans (WIPG) appeared to represent hyaluronic acid-dependent aggregates of the larger of the two WSPG. The proteoglycans contained approximately 87% chondroitin sulfate and 5% dermatan sulfate. Keratan sulfate could not be detected. Addition of ascorbate to the culture medium did not change the amount or the hydrodynamic size of the proteoglycan aggregates but did alter the quantity of the larger WSPG monomer synthesized depending upon the culture regimen used. Thus, these cells are capable of expressing their differentiated phenotype in short-term monolayer cell culture.