The nature of the laminin α chains in the embryonic and adult kidney is still being debated. The present study attempted to clarify this issue by immunofluorescence study using monoclonal antibodies against mouse α1, α2, and α5 chains and in situ hybridization for the α2, α3B, α4, and α5 mRNAs. Novel α1 chain‐specific monoclonal antibodies against E8 fragment revealed a restricted distribution of α1 chain in a subset of epithelial basement membranes in the embryo, in agreement with previous mRNA data. The α2 mRNA was produced by mesenchyme, although the protein was deposited in epithelial basement membranes. The α3B mRNA was found only in a small subset of endothelial cells. The α4 mRNA was found transiently in embryonic mesenchyme, with particularly high levels in condensed mesenchyme, close to the tips of the ureteric tree where tubulogenesis is initiated. The α5 mRNA was strongly expressed by ureter epithelium but not expressed at early stages of tubulogenesis. Immunofluorescence verified low levels of the α5 chain in the early stages of tubulogenesis. However, during the capillary loop stage, the α5 chain became strongly expressed in the developing glomerular basement membrane, which matches the in situ hybridization results. During subsequent maturation of the kidney, the α5 chain became ubiquitously expressed in basement membranes. Overall, the α5 chain exhibited the broadest pattern of expression, followed by the α1 chain, particularly in the adult stage. These chains were the only ones produced by epithelial cells. Although some basement membranes contained several α chains, we failed to detect any of the five studied chains in some basement membranes. Thus, the identity of the α chains of many embryonic kidney blood vessels and several basement membranes in the inner medulla in the developing and adult kidney remain unclear. Dev. Dyn. 1997;210:446–462. © 1997 Wiley‐Liss, Inc.