In this work, we implemented a qualitative and fast bioassay using the nematode Caenorhabditis elegans to detect the production of β-exotoxin in different strains of Bacillus thuringiensis. We show that this assay is useful to detect β-exotoxin in B. thuringiensis with high reliability, helping to discriminate strains that could not be used as bioinsecticides because of their putative risk to humans. Data show that qualitative bioassay with nematodes is a potential alternative to fly larvae bioassays, and correlated with the determination of β-exotoxin by HPLC.