ABSTRACT.We have determined the complete nucleotide sequence of the coding region of the small subunit rRNA gene of the hypotrichous ciliateEuplotes aediculatus.It is 1882 nucleotides long and contains several inserts not present in the small subunit rRNA genes of the hypotrichsOxytricha novaandStylonychia pustulata.A comparison of the sequences suggests thatE. aediculatusis much less closely related to these other two hypotrichs than they are to each other. Although the gene sequence ofE. aediculatusis drifting more rapidly than those of these other two species, its faster evolutionary clock is not enough to account for the degree of difference between them.