The half-life of spores and endocrystals of Bacillus thuringiensis Berliner on soybean leaves was less than 24 h, since 65% of the insecticidal activity, and 90% of the spore viability, was lost during the 1st day. However, some insecticidal activity could be detected at 7 days postapplication. The half-life of the nucleopolyhedrosis virus of Heliothis (Baculovirus heliothis) was >2 <3 days. Viral activity could not be detected after 14 days' exposure on soybean leaves.