Water soluble alkaloid (WSA) extracts from Chelidonium majus L. (great celandine) roots. growing on uncultivated ground in the Azores. were prepared. The WSA showed antibacterial properties towards Bacillus subtilis. The effect of WSA appeared to be 1/10 of tetracycline. For concentrations lower than 100 @disc, no reproducible sensivity was observed. Chelidonine, protopine and allocryptopine had no action against Bacillus subtilis. Coptisine, which is reported as not exhibiting antibacterial activity, showed activity against Bacillus subtilis in a similar way as sanguinarine and berberine. Chelerythrine was the most active alkaloid (about 40-50% higher than sanguinarine). Sanguinarine and chelerythrine are generally accepted as the alkaloids responsible for the antibacterial properties of Chelidonium latex. Results suggest that, at least for the species existing in the Azores, berberine and coptisine also contribute to that biological activity .