Skin biopsies were performed on female (NZB X NZW)F1 mice (B/W) at ages ranging from 1 to 12 months. The control strain was the C57B1/6. Immunoglobulin G and beta 1C globulin deposition was sought using the indirect immunofluorescence method. Both globulins were detected consistently at the dermal-epidermal junction from the age of 6 months. The pattern of staining was granular, and progressed from focal deposition to confluent and diffuse involvement of the basement membrane at 9-10 months of age. No staining was observed in any of the C57B1/6 mice up to 14 months of age. These findings increase the resemblance of B/W disease to human systemic lupus erythematosus.