C hromogranin A is an acidic protein costored and coreleased with catecholamines from storage vesicles. Its serum concentration is elevated in patients with peptide-producing endocrine neoplasia. We measured serum chromogranin A at the time of diagnosis in 34 children with all stages of neuroblastoma. With a sensitivity of 91% and specificity of 100%, serum chromogranin A emerged as a useful diagnostic tool for neuroblastoma, comparable to or better than other measurements such as neuron-specific enolase, ferritin, or dopamine-beta-hydroxylase. Mean serum chromogranin A correlated with disease stage (r = 0.76, P less than 0.01). The relationship of prognosis (progression-free survival) to baseline serum chromogranin A, age, and disease stage was determined in 34 patients at risk for relapse, with a median followup period of 18 mo (range, 1-48 mo). The survival rate for patients with lower serum chromogranin A levels (less than 190 ng/ml at the time of diagnosis) was 69%, whereas it was 30% for those with higher chromogranin A levels (P less than 0.05). Furthermore, when subjects were additionally stratified by either age or stage, chromogranin A was an effective prognostic tool in patients who either were older than 1 yr (P less than 0.005) or had more advanced disease (stage III or IV; P less than 0.05). We conclude that serum chromogranin A in neuroblastoma is (a) a valuable (sensitive and specific) diagnostic tool, (b) a correlate of tumor burden, and (c) a useful predictor of survival.