To clarify the relationship between uric acid urolithiasis and purine catabolites in newborn piglets, the incidence of uric acid urolithiasis and the plasma concentrations of xanthine, hypoxanthine, uric acid and allantoin were examined in 32 piglets. The newborn piglets were divided into two groups: normal (over 1.2 kg, n = 18, group N) and low body weight (below 0.9 kg, n = 14, group L). The animals in both groups were given water (non-nutrition, n = 11, treatment W), artificial milk (normal nutrition, n = 12, treatment M), or a combination of water and allopurinol (prophylactic treatment for the urolithiasis, n = 9, treatment A), during the first 60-hr of birth. At necropsy, the incidence of urolithiasis was higher in the piglets that received treatment W than those in the treatment M or A in both the N and L groups. In group L, the plasma xanthine, hypoxanthine and uric acid concentrations were markedly increased in the piglets that underwent treatment W compared with the treatment M. In both the N and L groups, the plasma allantoin concentration was higher in the treatment W piglets as compared with the treatment M piglets. These results suggested that the occurrence of uric acid urolithiasis in the newborn piglets is attributable to increased purine catabolites due to a starvational condition after birth.