The complete nucleotide (nt) sequence of the gene (rompA) encoding the 190-kDa immunodominant surface antigen (rOmpA) of Rickettsia conorii (Malish 7 strain) was determined. Sequence analysis revealed an ORF of 6063 nt encoding a deduced protein of 203,247 Da. Ten consecutive highly conserved repeat units, located at the 5' end of rompA, spanned 2.2 kb. Two types of repeats could be identified: type I of 225 bp, and type II of 216 bp. The order and number of repeats differed from those reported for R. conorii (Kenya tick typhus strain), R. akari (Kaplan strain) and R. rickettsii (R strain). Alignment of the R. conorii (Malish 7 strain) rompA gene with its R. rickettsii homolog revealed 95% nt sequence similarity. The conservation of rompA across several pathogenic spotted fever group (SFG) rickettsial species suggests that it may be a potential candidate for use as a subunit vaccine for SFG rickettsial diseases.