Screening for neuroblastoma at 3 weeks of age: methods and preliminary results from the Quebec Neuroblastoma Screening Project. A large neuroblastoma screening study was recently started in the province of Quebec, Canada. This project, a collaboration between the Quebec Network for Genetic Medicine and the University of Minnesota, is studying the impact of screening infants for the preclinical detection of neuroblastoma on the population-based mortality caused by this tumor. All infants born in Quebec during a 5-year period will be screened twice, at 3 weeks and at 6 months. Urinary homovanillic acid and vanillylmandelic acid determination from dried filter paper samples is used for screening. Initial qualitative screening is done by means of thin-layer chromatography with confirmatory quantitative screening by gas chromatography-mass spectrometry (GC-MS). During the initial 6 months of 3-week screening, 41,673 neonates (92% compliance rate) were screened and 10.6% of them were tested also by GC-MS. Nine of these neonates had positive results on two GC-MS tests and were referred for evaluation to rule out the presence of neuroblastoma. Four had the tumor, 1 had a calcified adrenal gland, and 4 had no tumor detected. Three additional neonates had clinical diagnosis of neuroblastoma before they reached the screening age of 3 weeks. A neuroblastoma that did not secrete homovanillic acid or vanillylmandelic acid was diagnosed clinically in 1 additional patient who tested negative by screening. 