We have observed that a fairly large amount of vanillylmandelic acid and homovanillic acid in urine samples taken randomly from patients with a tumor of about 10 g was less than the cutoff values and overlapped with the respective ranges of normal infants. Consequently, with only a single random urine sample there is a risk of overlooking a patient, especially in cases where the tumor is small. However, according to theoretical calculation, several random urine samples may enable us to discriminate a patient from a normal infant and can replace the 24-hour urine accumulation for 3 days which is currently performed for final judgement in the mass screening of neuroblastoma. urine sample randomly taken can replace the 24-hour urine specimen. In the present report, we investigate whether a patient can be discriminated from a normal infant by randomly sampled urine.