Addition of dibutyryl adenosine 3':5'-monophosphate (dcbAMP), colchicine or dbcAMP/colchicine to bone organ cultures markedly inhibited bone resorption. Calvaria of newborn mice labeled with 45Ca 3 days before sacrifice were removed and cultured in medium containing 3H-glucosamine. Both agents alone and in combination inhibited 45Ca release. DEAE-cellulose chromatography of the papa in-digested medium and bone resolved the 3H-glucosamine-labeled macromolccular material into four peaks. A marked increase in radioactivity was observed in the hyaluronate fraction (peak III) of the chromatographed bone samples. The results indicate that dbcAMP does not mimic the effect of parathyroid hormone on bone resorption, but that it is similar to colchicine in both the inhibition of bone resorption and the increased incorporation of 3H-glucosamine into hyaluronate. Although the role of hyaluronate. if any, in this experimental system remain elusive, the increased radioactivity associated with the hyaluronate fraction may be due to decreased degradation resulting from decreased hyaluronidase synthesis.