There are increasing evidences for the presence of an endogenous digitalis-like substance (EDLS) which interacts with the digitalis receptor and acts against the digoxin serum response in human body. The plasma EDLS level increases in response to fluid or salt loading. EDLS may play a role in salt and blood pressure regulation. Being considered as a volume-expanding state, pregnancy may cause an increase in maternal EDLS. However, further studies to identify the origin of EDLS in normal pregnancy are needed. There are increasing evidences for the presence of an endogenous digitalis-like substance (EDLS) which interacts with the digitalis receptor and acts against the digoxin serum response in human body. The plasma EDLS level increases in response to fluid or salt loading. EDLS may play a role in salt and blood pressure regulation. Being considered as a volume-expanding state, pregnancy may cause an increase in maternal EDLS. However, further studies to identify the origin of EDLS in normal pregnancy are needed.