To evaluate the effects of 12 biotic and abiotic elicitors for increasing the production of plumbagin in Plumbago indica root cultures. Most elicitors showed minimal effects on the root dry weight, except for 250 mg chitosan l(-1) and 10 mM l-alanine that markedly decreased root biomass by about 40 % compared to the untreated root cultures (5 g l(-1)). Treatments with 100 A mu M AgNO3 significantly increased intracellular plumbagin production by up to 7.6 mg g(-1) DW that was 4-fold more than the untreated root cultures (1.9 mg g(-1) DW). In contrast, treatments with 150 mg chitosan l(-1), 5 mM l-alanine, and 50 A mu M 1-naphthol significantly enhanced the extracellular secretion of plumbagin by up to 10.6, 6.9, and 5.7 mg g(-1) DW, respectively, and increased the overall production of plumbagin by up to 12.5, 12.5, and 9.4 mg g(-1) DW, respectively. Chitosan (150 mg l(-1)), l-alanine (5 mM), and 1-naphthol (50 A mu M) were the best elicitors to enhance plumbagin production in P. indica root cultures.