AbstractThe present study attempts to define the difficulties in evaluating the properties of the hemoregulatory peptide AcSDKP usingin vitroassays. In fact, in the presence of sera, which are generally added to basic culture media, AcSDKP is catabolized by proteases present in the serum. The kinetics of AcSDKP degradation depends on the nature and on the concentration of the added serum. Inin vitroconditions, the half life of this peptide can be increased by the addition of 1 M captopril, a metalloprotease inhibitor. Thus, these points need to be considered in designing experiments to study the effects of AcSDKP.