Vertebrate kidney development involves a series of complex interactions between the ureteric bud and undifferentiated mesenchyme resulting in the production of the nephron unit. These interactions are thought to be dependent on a variety of locally derived soluble factors, including peptide growth factors and their receptors. We have extensively analyzed the neurotrophins (NT) and their receptors during human kidney development. The neurotrophin receptors p75 and trk were both present within cells of early glomerular/tubular structures but absent from uninduced mesenchyme. Later in organogenesis, the NTs NT-3 and BDNF colocalized with their respective receptors in differentiated tubules. These findings suggested that the NT:receptor complex was not involved in the early inductive events of renal development but was responsible for postinductive tubulogenesis and epithelial integrity. In situ hybridization confirmed selective localization for the expression of trk B and trk C receptors and Western blot identified a full-length (kinase-active) trk receptor during human kidney development.