Purpose of work: The study was aimed to assess the antineoplastic activity of justicidin B in vitro and to search for its general toxicological profile in vivo. The anti-neoplastic activity of the arylnaphthalene lignin, justicidin B, was assessed in a panel of human lymphoma cell lines and compared with etoposide as a reference compound. A screening of the cytotoxicity after 24, 48 and 72 h exposure was performed by the MTT-dye reduction assay. Dose- and time-dependent cytotoxic effect was observed and the IC50 values ranged from 0.17 A mu M (RPMI-8226, 72 h) to 183 A mu M (U-266, 24 h) and more than 200 A mu M (HD-MY-Z, 24 and 48 h). Activation of caspase 3 and 8 was involved in the induction of programmed cell death in DOHH-2 cell line. NF-kappa B modulation occurred in DOHH-2 and HH cells. The general toxicity in mice after i.p. injection was also tested. The highest applied dose (50 mg/kg = 137.25 A mu M) did not show any toxicity. Justicidin B possesses definite and potent selective antineoplastic activity, related to its ability to induce programmed cell death in NHL-derived human cell lines at concentrations that can be reached in mice without toxicity.