Serum protein electrophoresis is commonly used in case of acute or chronic renal failure. It can lead to the etiologic diagnosis by detecting monoclonal gammopathies which are frequently complicated by renal failure, such as cast nephropathy, Randall's disease or amyloidosis, or to explore an associated inflammatory syndrome. We report the occurrence of two monoclonal components in a patient without any monoclonal component 10 days earlier. The sudden appearance of these two monoclonal components associated to the context of sepsis of urinary origin suggested the diagnosis of transient monoclonal gammopathy. This hypothesis was confirmed by monitoring serum protein electrophoresis that showed a gradual decrease of these two monoclonal components few weeks after the resolution of the infectious disease. The main etiological factors of transient monoclonal gammopathies are infectious or autoimmune diseases. In this context, it is important to delay the achievement of serum protein electrophoresis after the acute episode, in order to avoid to falsely conclude to hematologic malignancy diagnosis. This can prevent costly biological examinations of these transient monoclonal gammopathies and invasive procedures like bone marrow examination.