This study was undertaken to determine whether the cells of the fibrocartilaginous meniscal substance are capable of proliferation and matrix synthesis. Cells were isolated from the fibrocartilaginous menisci of young New Zealand white rabbits, and grown in two alternative culture regimens differing only in the basal nutrient medium used to initiate primary monolayer growth. Under each culture regimen, the cells attached and proliferated both initially and after passage into secondary (2 degrees) culture. Differences were noted in cell morphology and time to reach confluence in primary (1 degrees) culture. Upon passage into 2 degrees culture, the fibrochondrocytes assumed two distinct morphologies depending upon the type of medium used for 1 degree culture. These morphological changes were accompanied by differences in the population doubling time and incorporation of 35SO4 into sulfated proteoglycans. The proliferation of both fibrochondrocyte subtypes was stimulated by the addition of either pituitary fibroblast growth factor (FGF) or human platelet lysate in a dose-dependent manner. Both FGF (10 ng/ml) and ascorbate (40 micrograms/ml) decreased 35-sulfate incorporation, whereas only ascorbate was found to alter the amount of sulfated glycosaminoglycan in the pericellular coat. We conclude that the fibrochondrocytes of the meniscal substance are capable of replication and synthesis of matrix macromolecules if given the proper stimuli. Additionally, there may be two subpopulations of fibrochondrocytes that can be distinguished by their in vitro behavior.