Glycine-rich peptide toxin of cyanobacterium Scytonema MKU 106 was purified. UV spectral analysis showed an absorption maximum at 228 nm and the molecular mass was less than 12 kDa. The mortality rate of American boll worms (Helicoverpa armigera) was about 80% and 40% 84 h after treatment with 0.001% crude and purified peptide toxins respectively; 100% mortality was observed after 108 h treatment with both purified and crude peptide toxins. The LC(50) (lethal concentration to 50% of the population) for Heliothis larvae after 96 h was 8.3 mu g/ml purified peptide toxin and 6.2 mu g/ml crude peptide toxin. Observations also show that the peptide toxin at 0.01% concentration acts as a biopesticide and at high (0.1%) concentrations it will act as an anti-feeding compound for Stylepta derogata (leaf-roller) larvae of the cotton crop.