Urinary excretions of cystathionine, catecholamines, and vanillymandelic acid were compared in 27 patients with neuroblastoma and in nine other patients with non-neurogenic tumors. Eleven of the 27 patients were without clinical evidence of active neuroblastoma at the time of the study and excreted no or relatively small amounts of urinary cystathionine. Thirteen of the remaining 16 patients with progressive neuroblastoma had elevated cystathionine values. Elevated values were also detected in three of nine patients with other tumors. There was no correlation between the excretion of cystathionine and either catecholamines or vanillymandelic acid. The assay of cystathionine in addition to catecholamines and vanillymandelic acid is recommended for the complete biochemical evaluation of patients with neuroblastoma.