Neuroblastoma remains a significant problem in pediatric oncology. Recently a "multidrug-resistance" gene that may cause cells to become resistant to various chemotherapeutic agents has been cloned. The gene encodes the high-molecular-weight plasma membrane protein known as P-glycoprotein. To study the expression of this gene in cells exhibiting the multidrug-resistant phenotype, a panel of sublines selected with several different natural product drugs was established. The drug-sensitive parental BE(2)-C cells were clonally isolated from the human neuroblastoma SK-N-BE(2) line and exhibit a 150-fold increase in the copy number of the N-myc protooncogene. Sublines were selected by stepwise increases in the concentration of actinomycin-D, doxorubicin, vincristine, or colchicine. Gene amplification was assessed using Southern analysis, and RNA levels were determined by Northern and dot-blot analysis. Western blotting was used to determine protein levels. N-myc amplification and expression were simultaneously determined to assess possible alterations associated with development of multidrug resistance. Amplified P-glycoprotein-encoding genes were not seen in control lines but were clearly present in those that had undergone exposure to each of the chemical agents. Similarly, steady-state messenger RNA and protein levels were greatly increased in the drug-resistant sublines. We conclude that human neuroblastoma cells can acquire the multidrug-resistant phenotype after exposure to various chemotherapeutic agents.