The composition of crystal proteins and plasmid patterns in five new coleopterancidal strains of Bacillus thuringiensis were investigated. Larvae of Plagiodera versicolora were chosen as a model insect in bioassay. Strain YM-03 had the highest toxicity. Plasmid patterns were detected by rapid agarose gel electrophoresis. It was demonstrated that plasmid patterns of five Bt strains were quite different. The partial amino acid sequences of the N-terminal of crystal protein from YM-03 were analyzed by amino acid analyzer. A genomic library of delta-endotoxin of YM-03 was constructed. The EcoRI fragments (20-30 kb) from the total DNA were ligated with the vector DNA of pLAFRI. Thirteen clones which contained both of pLAFRI and foreign DNA fragments were obtained from 17 recombined plasmids. The frequency of recombinant clones was 76%. Three positive clones, LE392 (pBYM2), LE392 (pBYM3) and LE392 (pBYM4) were detected from 1200 resistant clones by using a synthesized 18bp probe from a coleopterancidal delta-endotoxin gene. It was shown that LE392 (pBYM3) and LE392 (pBYM4) had the same EcoRI digestion patterns and that they all contained coleoptera-specific delta-endotoxin gene but showed a different level of expression.