The whitefly Bemisia tabaci contains a primary prokaryotic endosymbiont housed within specialized cells in the body cavity. Two DNA fragments from the endosymbiont, totaling 33.3 kilobases, were cloned and sequenced. In total, 37 genes were detected and included the ribosomal RNA operon and,genes for ribosomal RNA proteins. The guanine plus cytosine of the DNA was 30.2 mol%, different from that of endosymbionts of other plant sap-sucking insects.