AbstractThe ability of cyclic adenosine monophosphate (cAMP) to maintain differentiated properties of canine articular chondrocytes in culture is reported. Treatment with 0.5 mMdibutyryl cAMP (DBcAMP) caused the cells to adopt a more rounded morphology. This change in morphology seems to have no effect on the overall biosynthetic rates of the cells. After a pulse with35S‐methionine, there was no difference in the concentration of labeled proteins between cultures treated with DBcAMP and control cultures. After 6 days, the amount of fibronectin (FN) in the media of DBcAMP‐treated cultures detected by an enzyme‐linked immunosorbent assay was specifically reduced by 30%. The amount of35S‐FN purified by gelatin‐affinity chromatography decreased 33%. Moreover, the percentage of FN containing the extra domain A sequence was reduced from 19.4 ± 8.7% in control cultures to 9.6 ± 4.2%. Concomitant with the decrease in FN, there was an increase in the concentration of keratan sulfate in the media of DBcAMP‐treated cultures. After 6 days, treated cultures had 47% more keratan sulfate than controls did. These changes appear not to be the result of a change in the deposition of FN or keratan sulfate, because the amount of these molecules that could be extracted from the cell layer was typically below the limit of detection of the assays. Instead, it seems there is a phenotypic change in the chondrocytes pertaining to the production of FN and ke