Burkholderia cepacia H111, which was isolated from a cystic fibrosis patient, effectively kills the nematode Caenorhabditis elegans. Depending on the medium used for growth of the bacterium two different killing modes were observed. On high-osmolarity medium the nematodes became paralysed and died within 24 h. Using filter assays we provide evidence that this killing mode involves the production of an extracellular toxin. On nematode growth medium killing occurs over the course of 2-3 days and involves the accumulation of bacteria in the intestinal lumen of C. elegans. We demonstrate that the cep quorum-sensing system of H111 is required for efficient killing of C. elegans under both killing conditions. Using the C. elegans phm-2 mutant that has a non-functional grinder evidence is provided that the cep system is required to enter the intestinal lumen but is dispensable for the colonization of the gut. Furthermore, we demonstrate that the type II secretion machinery is not essential for nematode killing.