The effect of N6-2O-dibutyryl cyclic AMP (db-cyclic-AMP) on erythropoiesis in NMRI mice was investigated. This effect was measured by the incorporation of 59Fe into peripheral blood, spleen, and bone marrow. The study included plethoric as well as normal mice. Route of administration and dose schedule were varied. In spite of this, we were unable to demonstrate any stimulating effect of db-cyclic-AMP on erythropoiesis.