Three new imidazole alkaloids, leucettamines A [1] and B [2] and leucettamidine [3], have been isolated from the Palauan sponge Leucetta microraphis. Their structures were established on the basis of extensive spectral analyses. Leucettamine A showed potent leukotriene B4 receptor binding activity (Ki = 1.3 μM), while leucettamine B was essentially inactive (Ki = 100 μM) and leucettamidine showed significant activity (Ki = 5.3 μM). With leucettamine A identified as a pure LTB4 receptor antagonist, a new structure lead is presented to inflammation therapy.