The cyclic hexadepsipeptide beauvericin, initially known as a secondary metabolite produced by the entomopathogenic fungus Beauveria bassiana and toxic to Artemia salina larvae, has been more recently recognized as an important mycotoxin synthesized by a number of Fusarium strains, which parasite maize, wheat and rice. Therefore, this mycotoxin may enter the food chain, causing yet unknown effects to the health of both domestic animals and humans. The cytotoxic effects of beauvericin on mammalian cells have been studied. We investigated the cytotoxicity of this compound in an in vitro invertebrate model, viz. the insect cell line SF-9 (immortalized pupal ovarian cells of the lepidopter Spodoptera frugiperda). Cultures of SF-9 cells in the stationary phase were exposed to beauvericin at concentrations ranging from 100 nM to 300 M, for different periods of time (from 30? to 120 h). The effects on cell viability were assessed by the trypan blue exclusion method. After 4 h of incubation no significant decrease in cell viability was recorded in SF-9 cell cultures exposed to low concentrations of beauvericin, i.e. 100 nM and 300 nM. However, a slight decrease in viability (3.9%) was seen already in cells exposed to the mycotoxin at the 1 M concentration. This effect became gradually more evident at higher concentrations ( 28% at 30 M, 50% at 100 M, 68% at 300 M). An even more pronounced reduction in cell viability was observed after a 24 h exposure. Under these conditions, 1 M beauvericin caused an approx. 10% decrease in the number of viable cells, which became more significant at higher concentrations 23% at 3 M, 47% at 10 M, 65% at 30 M, 90% at 100 M, 99% at 300 M). Therefore, the 50% cytotoxic concentrations (CC50) at 4 h and 24 h could be estimated as 85 M and 10 M, respectively. In time-course experiments, no effect of beauvericin (30 M) on cell viability could be seen after exposure for periods of time as long as 30?, 1 h and 2 h, respectively. In contrast, when SF-9 cells were exposed to the mycotoxin for longer periods of time, from 8 h to 120 h, we recorded a strong cytotoxic effect already in the low micromolar concentration range. Thus, the CC50 after both 72 h and 120 h exposure times was assessed as 2.5 M. Higher concentrations caused a virtually 100% cell death. The data collected suggest that beauvericin exerts a substantial dose- and time-dependent cytotoxic effect on invertebrate cells, comparable to the effects described in mammalian cells.