Biochemical changes produced by luxabendazole in muscle-stage Trichinella spiralis larvae consisted of a decrease in free glucose and glycogen levels (46.71% and 35.66%, respectively) after in vivo treatment, slight in vitro inhibition of fumarate reductase activity (24.15%) and, finally, inhibition of [3H]-colchicine-tubulin binding, which was found to be of a competitive nature, with an inhibition constant (Ki) of 0.9 x 10(-7) M. In a parallel study, luxabendazole did not appear to be inhibitory to [3H]-colchicine binding to pig-brain tubulin.