Objective - To evaluate expression of the α6 chain of type IV collagen in the glomerular basement membranes (GBM) of healthy dogs. Sample Population - Kidney specimens from 12 healthy dogs. For comparison, kidney specimens from 8 human subjects between 25 and 83 years old also were evaluated. Procedure - Sections were immunolabeled with a monospecific antibody that cross-reacts with human and canine α6(IV) chains and examined by means of fluorescence microscopy. Results - Immunolabeling of the α6(IV) chain was not observed in GBM of 6 dogs ≤ 30 months old but was observed in GBM of the remaining 6 dogs, all of which were ≥ 45 months old. Expression of the α6(IV) chain was not observed in GBM of the human subjects, regardless of the age of the subject. Conclusions and Clinical Relevance - Results indicate that the α6(IV) chain is expressed in GBM of healthy dogs, but the expression is age-dependent. Composition and structural organization of type IV collagen in the GBM of healthy adult dogs is different from that described for other species. (Am J Vet Res 2000;61:38-41).