The mortality of non-target organisms during efficacy tests of Bacillus thuringiensis var. israelensis against Simuliid larvae was evaluated in a small stream in Newfoundland. Three applications of about 1 X 105 cells/ml were made during the spring and summer of 1979. Non-target insects occurring on stones with Simuliids were sampled within 24 hr prior to treatment and from 3 to 7 days post treatment. The results indicated there were no significant decreases in the major groups of non-target insects that could be directly accounted for by the treatments. On the other hand the Simuliids in the last 2 treatments had an overall mortality of more than 93% in the zone sampled.