Many diseases involve hematuria, and a few of these diseases occur in the setting of an upper respiratory infection or of upper respiratory signs and symptoms. When hematuria follows within 2 days of the onset of an upper respiratory infection without skin lesions in a young patient, IgA nephropathy (Berger's disease) should be considered. This disease involves the deposition of IgA in the mesangium of the glomeruli. Light microscopic examination may suggest the disease, but renal biopsy immunofluorescence (IF) must be performed to confirm it. This disorder may be the most common cause of nephritic syndrome worldwide. The hematuria may become recurrent, with proteinuria that may approach nephrotic syndrome propoions. Serum levels of IgA may be elevated. A small percentage of patients may progress to renal failure over a period of years. In contrast to Berger's disease, a linear IF pattern suggests a type II hypersensitivity reaction, such as Goodpasture's disease, while a granular pattern is seen with poststreptococcal glomerulonephritis (GN), membranous GN, focal segmental glomerulosclerosis, and membranoproliferative GN. Most positive immunofluorescence patterns involve IgG and C3, except that a granular IgM pattern is present in focal segmental glomerulosclerosis, while mesangial IgA is seen in IgA nephropathy (Berger's disease). Lipoid nephrosis would have a negative IF pattern; that is, there would be no staining present.