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Two subspecies of Bacillus thuringiensis, ssp. israelensis (BTI) from the Negev Desert of Israel, and the PG-14 isolate of ssp. morrisoni (BTM PG-14) from Cebu City in The Philippines, produce mosquitocidal parasporal bodies with similar but not identical protein complements. To investigate the relatedness of the proteins which occur in the parasporal bodies of these two isolates, we cloned and sequenced the genes encoding a 72,000 M(r) protein (CryIVD gene) and an associated protein of 20,000 M(r) located 279 base pairs downstream. The nucleotide sequence of the open reading frame for the BTM cryIVD gene differed from that of the corresponding BTI gene at a single position (1764; T in BTI, C in BTM PG-14), but the resulting codon encoded the same amino acid (valine). The nucleotide sequence of the open reading frame for the 20,000 M(r) protein of BTM PG-14 contained two substitutions in comparison to BTI, C for T at position 54, and G for T at position 384, but neither of these substitutions resulted in a change in the amino acid encoded. These results demonstrate that a remarkable degree of conservation exists among the genes encoding CryIVD and 20,000 M(r) proteins of BTI and BTM PG-14, suggesting that the plasmid encoding these genes has a common origin and perhaps was transmitted from one subspecies to the other during their recent evolutionary past.