The addition of a 1 mM N6, O2'-dibutyryl cyclic AMP to incubations of foetal calf articular cartilage for a 4 h period resulted in a 13 and a 15% decrease, respectively, in the rate of incorporation of [3H]glucosamine and [14C]glucose into glycosaminoglycans. Under the same conditions, a 41% increase in the rate of incorporation of [35S]sulphate into glycosaminoglycans was observed. Dibutyryl cyclic AMP had no effect on protein synthesis over a 4 h period or on the hydrodynamic size of the proteoglycan subunits or glycosaminoglycans synthesized by the cartilage. When the glycosaminoglycans were digested with chondroitin ABC lyase and the resulting disaccharides analysed on Dowex 1 (formate form), it was observed that dibutyryl cyclic AMP increased the degree of sulphation of the disaccharides. Furthermore, an over-sulphated disaccharide corresponding to chondroitin 4,6-disulphate was identified. It was concluded that dibutyryl cyclic AMP was stimulating the process of sulphation of glycosaminoglycans by cartilage.