The biological effects of the pyrazolyl-ureas and dihydro-imidazo-pyrazolyl-ureas (STIRUR 13, STIRUR 41 and BUR 12) were tested on two NB cell lines with a different status of MYCN oncogene activation, namely ACN (without MYCN amplification) and HTLA-230 (with MYCN amplification) cells. The gene discussed is MYCN; the disease is neuroblastoma.