The stability of [(N-pyrrolidine)metylene]daunorubicin (PMD) in aqueous solutions was studied in the pH range 0.42-12.03 at four temperatures. Its degradation was evaluated by using an HPLC method with UV detection (254 nm). The hydrolysis of PMD involved: (a) hydrolysis of protonated molecules of PMD depending on hydrogen ions and (b) spontaneous hydrolysis under the influence of water depending on the substrate charge.