Crystalluria, medullary matrix crystal deposits and bladder calculi associated with an acutely induced renal papillary necrosis. A single (100 mg/kg) intraperitoneal dose of 2-bromoethanamine hydrobromide induced renal papillary necrosis (RPN) acutely in rodents and caused a transient crystalluria between 4 and 8 h after dosing. These crystals comprised struvite or magnesium ammonium phosphate (MAP) as assessed by shape, solubility, infra-red spectrum and X-ray microprobe analysis. Acid-soluble, bi-refringent crystals were also present within the renal medullary matrix during the same time period as the crystalluria. The presence of the MAP was associated with loss of the anionic renal medullary mucopolysaccharides staining. A total of 5/64 rats with a 2-bromoethanamine-induced renal papillary necrosis and monitored for up to 160 days had bladder calculi that were predominantly MAP. These data suggest that medullary mucopolysaccharide matrix disruption associated with RPN leads to a release of previously bound cations, super-saturation and the nucleation of crystalline MAP. These processes could also be implicated in the formation of MAP bladder calculi. 