Due to its pivotal role in leukotriene biosynthesis the human 5-lipoxygenase (h5-LO) is involved in the development of inflammation, allergies and cancer. Novel 1,2,4-triazin-5-ones were both tested for their h5-LO inhibitory activity in intact neutrophile granulocytes and for their antiproliferative activity towards the chronic myeloid leukemia cell line K-562. Unexpectedly, all compounds showed only weak anti-leukotriene activity, whereby for some substances a moderate growth inhibiting effect towards K-562 could be observed. During the past years of searching for h5-LO inhibitors, the C2-like domain of h5-LO has attracted increasing attention as potential drug target. Amine- and photoreactive cross-linkers combined with nano-HPLC/MALDI-TOF/TOF mass spectrometry were employed to conduct conformational studies in-solution of recombinant C2-like domain alone as well as in the ligand-bound form.