Despite the common practice of upper gastrointestinal endoscopy, the unique 
phenomenon of punctate black pigmentation of the duodenal mucosa, now known as 
pseudomelanosis duodeni, still remains a rare entity. Four patients with normal 
renal function at presentation were found to have this pigment on endoscopy. One 
developed renal failure subsequently but the pigmentation persisted and this 
observation has not been reported before. Histochemical and ultrastructural 
studies were made. It is postulated that the pigment is heterogenous and 
represents a form of stored iron. Anti-hypertensive drugs may have a role in the 
causation of the pigmentation formation.