Three urea analogues, diflubenzuron (1 - (4- Chlorophenyl) -3- (2,6-difluorobenzoyl) urea), Bay SIR6874 (1-[3,5-dichloro - 4- (4-nitroophenoxy) phenyl] -3- (2- chlorobenzoyl)-urea), Bay SIR8514 (1 - (4-trifluoromethoxyphenyl) -3 - (2- chlorobenzoyl urea) and a JHanalogueStaufferMV-678 (2-methyl-9 - (p-isopropyl phenyl)- 2,6 - dimethylnonane), were compared for activity at 0.02 ppm Ai/1h against late instars of Simulium vittatum. Mean % mortalities of 70, 100, 86 and 45% were observed respectively. Some abnormalities produced in larvae by the urea analogues are discussed. Bay SIR 6874 produced mean mortalities in 72-96 h-old S. vittatum eggs of 15 and 50% at 0.1 and 0.2 ppm/24 h respectively. Diflubenzuron produced 100% mortality in eggs of the same age at 0.2 ppm/24 h.