The survival and distribution of Bacillus thuringiensis in farmland soil were analyzed. First, the survival of B. thuringiensis in soil was examined after spraying with the BT-microbial pesticide formulation and spores of B. thuringiensis , Aizawai (H-7) or Kurstaki (H-3a3b3c) isolates from the formulation onto the surface of 1 m² of fields for vegetables. The spore counts of B. thuringiensis increased more or less in any fields immediately after the spray. However, the count decreased by approximately log 1 within 1-4 weeks. Thereafter, the number of spores remained constant at the level of 10⁴ cfu/g for 8-12 months. B. thuringiensis , Aizawai and Kurstaki each maintained their ability to form parasporal crystals during residence in soil. Secondly, the distribution of B. thuringiensis was examined in various types of soils collected from 257 fields in Japan. Whether those fields had previously been treated with the BT pesticides was unknown. More than 80% of total samples contained B. cereus/thuringiensis at the levels of 10⁴-10⁶ cfu/g. Of 1, 906 B. cereus/thuringiensis strains from soil samples, 40 (2%) were identified as B. thuringiensis , due to the presence of the parasporal crystals. B. thuringiensis isolates were serotyped by means of the tube agglutination test with anti H sera of 32 known serovars. Consequently, all 40 strains were typed; they consited serovars H-3a3b3c (15 strains), 3a3d (12), 5a5c (1), 6a6c (4), 8a8c (1), 11a11c (5) and 13 (2). Among these serovars, serovar H-3a3b3c ( B. thuringiensis, Kurstaki ) which is formulated usually in the BT pesticides was isolated from 14 (5%) of 257 fields.