Autologous serological screening of a cDNA expression library (SEREX) derived from childhood neuroblastoma led to the identification of 10 different antigens, including 6 novel gene products. The novel antigen 018INX was derived from a small open reading frame in a region of α-internexin mRNA that was previously described as 3′ untranslated region. 018INX thus represents a novel type of tumor antigen. Five novel gene products were derived from NNP-1 (NNP3) and Hu genes (HuC-L, HuD3, HuDY, HuD1proc). As indicated by sequence analysis, these antigens were generated by alternative splicing and/or alternative promoter usage or allelic polymorphism. mRNA expression analyses revealed different tissue restrictions of novel compared to known HuD and NNP-1 transcripts in normal and malignant tissues. The expressions patterns of distinct transcripts indicated potential clinical meanings as diagnostic and/or prognostic tissue markers. When kinetics of serum antibody titres against SEREX-defined antigens were compared to tumor load over time in our patient with neuroblastoma, we found 100-fold increases of anti-Hu and anti-018INX antibody titres preceding the clinical diagnosis of recurrent tumor growth after 2 years. When sera of pediatric patients with cancer (30) and healthy controls (30) were tested for humoral responses to SEREX-defined neuroblastoma antigens, we detected antibodies against all known antigens and NNP3 with low frequencies and titres in control sera, while anti-018INX and anti-Hu antibodies were found in cancer patients only. Our findings indicate that SEREX-defined tumor antigens might provide novel tools for understanding and treatment of this aggressive childhood malignancy. © 2002 Wiley-Liss, Inc.