P-glycoprotein (P-gp) overexpression reduced the <i>in vitro</i> cytotoxicity of narciclasine less than that of another known P-gp substrate, vincristine.<h4>Conclusion</h4>Narciclasine demonstrates metabolic stability in human liver microsomes and hepatocyts, and its cancer cell penetration is minimally affected by P-glycoprotein. The gene discussed is ABCB1; the disease is cancer.