Abstract: Cyanobacteria are components of commercial fertilizers which may interfere with plantphysiology, making plants less susceptible to biotic and abiotic stress. A peculiar extract of theNostoc sp. BEA 0300B demonstrated to induce systemic resistance in zucchini plants againstPodosphaera leucotricha in previous biological and biochemical assays. The aim of this researchwas to investigate the behaviour of different chitinase isoforms in zucchini plants treated by foliarapplication of Nostoc sp. BEA 0300B extract. Chitosan was used as positive control, since it is awell-known resistance inducer, while untreated plants were used as negative control. Nostocextract (2g/l) was applied by spraying one of the 2 cotiledonar leaves. Total proteins wereextracted from untreated cotiledonar leaves sampled after 1, 2 and 3 days from the treatment, andwere examined with isoelectric focusing analysis. The specific assay for chitinases showed threeisoforms with 4.4, 4.6 and 4.7 isoelectric points that were enhanced by Nostoc treatment,depending on the sampling time.