Much research has been performed to gain better insight into the regeneration process, responsible for the functional and morphological recovery after acute renal failure (ARF). Many investigators focused on endogenously produced polypeptide growth factors as the major mediators of tubular epithelial cell proliferation. However, arguments contradicting this hypothesis have recently gained more support. Indeed, the early decrease of renal epidermal growth factor (EGF) and insulinlike growth factor-1 (IGF-1) in different experimental models of ARF has been frequently shown at both the mRNA and protein level, while other growth factors could not be shown to increase. Moreover, the inaccessibility of the upregulated receptors for endogenously produced growth factors has encouraged research to seek alternative origins for the signals inducing renal regeneration. The accumulation of mononuclear leukocytes in the renal interstitium is a striking observation in renal failure. Where the interstitial disease, recognized by the persistent interstitial accumulation of leukocytes, is a better predictor of chronic renal failure and developing fibrosis, ARF distinguishes itself by the disappearance of the infiltrate when regeneration is complete. The existence of a regenerative potential provided by the network of inflammatory mononuclear leukocytes is supported by studies on tissue repair in different fields. This review discusses the infiltrating network of mononuclear leukocytes as a major participant in the regeneration process after acute renal failure, including the approach which can be followed to investigate this hypothesis.