To assess glomerular filtration rate (GFR) in dogs naturally infected by D. immitis new renal marker serum cystatinC (sCysC) was measured with canine CysC ELISA kit. Twenty infected microfilaremic-seropositive and 20 amicrofilaremic and seronegative dogs evaluated in the study. Serum urea and creatinine (sCre) concentrations were measured in both groups. Mean sCysC concentrations in infected dogs were detected as 2.40 mg/L and 2.30 mg/L in controls. Mean serum urea 9.97 mmol/L and sCre 116.24 mu mol/L concentrations in infected and in the uninfected group detected as 11.92 mmol/L and 128.62 mu mol/L, respectively. Including mean sCysC and sCre concentrations with mean serum Urea:Cre ratio were not statistically differed between the groups. On the other hand, serum urea concentrations were statistically differed between groups. Based on the results of the present study, it is concluded that, sCysC concentrations seemed to be not altered in dogs with D. immitis infection.