Abstract Structure activity studies against filariae are described for a series of derivatives of 6- (3-aminophenyl)-2, 3, 5, 6-tetrahydroimidazo [2, 1-b] thiazole (15 derivatives. In an in vivo assay using gerbils implanted with both Acanthocheilonema viteae and Brugia pahangi, the former parasite was shown to be the more sensitive to a range of amides of 15. None of these compounds, however, had any activity at 5× 10− 5 mol against the worms in vitro ...