A local isolate of Bacillus thuringiensis (B.t. 81) contained five distinct plasmids Relative amounts of these plasmids varied at different stages of growth.Two Cry- mutants of the strain maintained all plasmids. The mutants, however, exhibited some variations in the patterns of large plasmids depending on the composition of culture medium even though they failed to produce crystal protein. Restriction analysis of the plasmids was also carried out for future cloning studies.