Background: The purpose of this study was to assess the efficacy of three chemotherapeutic agents both new and old, on a human neuroblastoma xenograft, designated TNB9, according to the standard Battelle Columbus Laboratories protocol. Cytogenetic and phenotypic analyses showed that TNB9 was one of the most malignant strains among human neuroblastoma xenografts. Methods: When the estimated TNB9 tumor weight reached 100 to 200 mg, 28 nu/nu BALB/c tumor- bearing mice were randomly divided into 4 groups. One of three drugs was administered intraperitoneally in a total of three doses at four-day intervals to the mice in each experimental group while the control group received injections of normal saline. The doses of these agents at each injection were equivalent to one-third of the LD50. The results were evaluated on the basis of the maximum inhibition rate and also by the degree of tumor regression. Results: Maximum inhibition rates were as follows: mitomycin C, 95.6%; irinotecan (CPT-11), 72.5%; paclitaxel, 46.4%. Mitomycin C was graded as having effects, representing tumor regression. Irinotecan was also effective against TNB9, and none of the irinotecan treated mice lost weight, suggesting minimal toxicity. Conclusions: Assessment of the chemotherapeutic sensitivity in vivo showed that irinotecan, mitomycin C were active agents whereas paclitaxel had minimal or marginal activity in the treatment of neuroblastoma.