20 guinea pigs, 10 of which were reported polydipsic by the owners (PD group) and 10 with normal water intake (C group) were examined for renal disease. After clinical examination the guinea pigs were anaesthetised, blinded and randomized and underwent renal ultrasonography, urine and blood sampling. The ultrasonographic findings were classified as 0 for no abnormalities indicative of renal dysfunction and 1 for abnormalities indicative of renal dysfunction. The C and PD group were subdivided into a C0, C1, PD0 and PD1 group according to these findings. Blood was analysed for urea, creatinine, glucose, fructosamine and PCV. Urine was analysed on urine dipstick for pH, blood, protein, glucose and density and a microscopic examination was done. The results were analysed and the groups were tested against each other for statistic significance by a Kruskal-Wallis and a Dunn's test (p<0.05). 2 animals from the PD group were euthanised and the kidneys sent for histopathology. 4/10 animal had renal changes on ultrasonography, all from the PD group, giving 3 groups: C0 (n=10), PD0 (n=6) and PD1 (n=4). Blood test results showed no statistic significance between groups for all tested parameters. Urine test results showed pH >8.5 and no glucose in 20/20 samples. For density and protein no statistic significance between groups were found. Blood was found on dipstick in 12/20 urine samples evenly distributed between groups. On microscopy red blood cells were found only in 4/20 samples, all 4 were positive for blood on dipstick. Histopathology of kidneys showed bilateral chronic nephrosclerosis in both cases, which correlated well with the ultrasonographic findings. In conclusion blood and urine tests do not seem as good diagnostic tools as in dogs and cats. Other parameters as serum amylase could be considered. Ultrasonography seems useful for diagnosing renal disease in guinea pigs, but further investigation is needed.