The structural gene encoding the 16S rRNA of the new obligate intracellular organism presently designated WSU 86-1044T was sequenced and analysed to establish its phylogenetic relationships. The 16S rDNA sequence was most closely related to those of chlamydial species, having 84·7–85·3 % sequence similarity, while it had 72·4–73·2% similarity with rickettsia-like organisms. When the sequences of the four species of chlamydiae (Chlamydophila psittaci, Chlamydia trachomatis, Chlamydophila pneumoniae andChlamydophila pecorum) were compared, they had > 93% sequence similarity indicating that WSU 86-1044T was not close enough to be in the same family as currentChlamydiaceae members. However, based on the 84·7–85·3% 16S rDNA sequence similarity of WSU 86-1044T and other previously described characteristics, WSU 86-1044T belongs to a novel family within the orderChlamydiales; hence, the proposal ofWaddliaceae fam. nov.,Waddlia chondrophila gen. nov., sp. nov.