We conclude (a) that, though levels of greater than 100 ng ml-1 are highly suggestive of advanced neuroblastoma, caution should be exercised in using serum NSE as a diagnostic test in children with cancer and (b) that serum NSE levels are not a sensitive index of residual neuroblastoma in patients, with initially elevated levels, that are receiving treatment. This evidence concerns the gene ENO2 and neuroblastoma.