We investigated whether the conditional, wound-inducible production of a Bacillus thuringiensis (Bt) Cry endotoxin may provide a hopeful and efficient alternative of protection from stem borer damage to the high dosage, constitutive or tissue-specific toxin delivery approach generally used in transgenic Bt crops. A synthetic cry1B gene controlled by the promoter region of either the constitutive ubiquitin (ubi) gene or of a wound-inducible proteinase inhibitor (mpi) gene from maize was introduced in rice by microprojectile bombardment. Accumulation of Cry1B from undetectable level to 0.2% of total soluble protein, 8-12 hours after mechanical wounding, was demonstrated in leaf and pith tissues of lines harbouring the pmpi-cry1B construct. In these plants, Cry1B was not detected in pollen and seed endosperm and embryo, unlike in pUbi-cry1B plants. Two out of 43 pmpi-cry1B plants were found to exhibit full protection against SSB damage. Field evaluation with artificial and natural infestations of the most promising ubi-cry1B and mpi-cry1B lines in Delta Del Ebre, Spain during the summer crop season 2001 confirmed the level of protection observed in greenhouse assays.