Aqueous suspensions of formulated Bacillus thuringiensis (H-14) wettable powder (Bactimos WP) and B. sphaericus (1593) acetone precipitated spore powder were compared with slow release floating pellet formulations of each pathogen for the control of Culex quinquefasciatus breeding in urban settings. In 15 and 8 liter buckets both suspensions provided complete control at 1 mg of powder/liter but suppression was brief with the B. thuringiensis (H-14) WP. Bactimos primary powder formulated into small, floating pellets (0.17 g primary powder/pellet), provided limited control for several weeks and was markedly inferior to the Bactimos briquette. One half briquette gave complete control for 3 weeks but its effectiveness declined as the briquette constituents sank. All B. sphaericus treatments provided continuous good to excellent control for the 8 weeks of observation. The best control in the 15 liter buckets was effected with 2 floating pellets each containing 0.21 g of B. sphaericus spore powder.