We present QNet, a method for constructing split networks from weighted quartet 
trees. QNet can be viewed as a quartet analogue of the distance-based 
Neighbor-Net (NNet) method for network construction. Just as NNet, QNet works by 
agglomeratively computing a collection of circular weighted splits of the taxa 
set which is subsequently represented by a planar split network. To illustrate 
the applicability of QNet, we apply it to a previously published Salmonella data 
set. We conclude that QNet can provide a useful alternative to NNet if distance 
data are not available or a character-based approach is preferred. Moreover, it 
can be used as an aid for determining when a quartet-based tree-building method 
may or may not be appropriate for a given data set. QNet is freely available for 
download.