Hyaluronan (HA), a glycosaminoglycan involved in many biological processes (i.e. cell migration and differentiation, regulation of extracellular matrix organization, inflammation) is synthesized by hyaluronan synthases and degraded by hyaluronidases (Hyals), mainly Hyal1 and Hyal2 in somatic tissues. Since intrarenal HA is mainly restricted to the inner medulla, where HA has been hypothesized to play a role in water handling, our aim was to determine to what extent the contribution of Hyal1 and Hyal2 in HA metabolism could modulate urine concentration. To do so, the renal phenotype of Hyal1^-/- and Hyal2^-/- mice was analysed in baseline conditions, during 24 hours water deprivation (WD) or after acute water loading (2 ml sterile water i.p.). Our results indicated that, compared to wild-type littermates (n=20), Hyal1^-/- mice (n=20) are characterized by a significant lower urine output (DUV= -25%), a higher urine osmolarity (DUosm=15%) and lower Na⁺ and K⁺ excretion rates (D= -27% and -34%, respectively). In contrast, baseline renal parameters were similar in Hyal2^-/- (n=16) vs Hyal2^+/- mice (n=20). After WD, a significant reduction in UV was observed, which was more pronounced in Hyal1^+/+ mice (D= -65 vs -40%, P=0.02, n=9), and the expected increase in Uosm only occurred in Hyal1^+/+ mice. In Hyal2^+/- and Hyal2^-/- mice, changes induced by WD were similar in both strains, averaging -60% and +65% for DUV and DUosm, respectively. In response to the test of acute water loading, all Hyal1^+/+ mice (n=9) started to excrete water during the first hour, whereas none of the Hyal1^-/- mice (n=9) produced any urine, as it was also the case in Hyal2^+/- (n=10) and Hyal2^-/- mice (n=10). Nevertheless, the total excreted volume of water was similar in the four groups, averaging 1200 ml after 6 hours. In summary, these observations could indicate that Hyal1^-/- mice present some impairment in the urine concentration mechanisms whose underlying processes have to be further investigated.