This preliminary study concerns murine monoclonal antibodies (Mabs) against tubular basement membranes (TBM) of human kidney which were produced by the classical hybridization technique. One of these Mabs (PP8–1) specifically recognized an antigen present in the tubular basement membranes of various portions of tubule and in the Bowman’s capsule. By immunocytochemical techniques, this Mab was used to study the presence and the distribution of the related antigen in urinary sediment from 12 normal healthy subjects. This TBM and Bowman’s capsule antigen was demonstrated along hyaline urinary cast surface and, in some cases, in free extracellular fibrillar structures morphologically unrelated to the casts. This suggests that, in some normal conditions, catabolism of TBM and/or Bowman’s capsule could release material in urine, as it has been described for glomerular basement membrane (GBM) constituents. Such an immunocytochemical approach could be useful to detect components from tubular renal basement membranes in urinary sediment during pathological conditions.