Three granular formulations of Bacillus thuringiensis var. israelensis were assessed in the summer of 1983. Evaluations included artificial pool studies, field trials and a prehatch/preflood trial in artificial pools. All products provided good control, especially of the floodwater species Aedes vexans and Ae. trivittatus. Residual activity was lacking in all products. Reinfestation was common in Culex breeding areas within 72 hr posttreatment. Prehatch treatments provided good control when flooded 1 hr after application; poor control occurred when pools were flooded 144 hr (6 days) after application.