The accumulation of hyaluronan (HA) in the renal cortex is a characteristic feature of inflammatory renal diseases. Fragments of HA derived from high molecular weight precursors are known to display inflammatory effects in vitro and could, therefore, participate in immune renal injury. To understand the mechanisms of HA fragmentation in vivo we examined the expression of recently characterized mammalian hyaluronidases in normal and autoimmune kidneys and in cell lines. We found that transcripts for the lysosomal–type hyaluronidases Hyal1 and Hyal2 were constitutively expressed in normal and autoimmune kidneys as well as in tubular epithelial cells and in a macrophage cell line. The expression of hyaluronidase genes in the cell lines did not increase in response to treatment with tumor necrosis factor alpha or gamma interferon. Interestingly, transcripts for the testicular–type hyaluronidase PH–20 (Spam1, Hyal3) were also detected in normal and autoimmune kidneys as well as in tubular cells and macrophages. Transcript levels were higher in kidneys from male mice as compared with age–matched females. Again, transcript levels did not change in vitro in response to cytokines. We conclude that mRNA for three different hyaluronidases is found in murine kidneys. The functional role played by these hyaluronidases in the degradation and metabolism of HA remains to be investigated further.