Historically, members of the Anopheles gambiae complex from Ethiopia have been identified chromosomally as either A. arabiensis or A. quadriannulatus. Recent collections from the Jimma area in Ethiopia, southwest of Addis Ababa, revealed 29 specimens of A. quadriannulatus based on the standard polymerase chain reaction (PCR) identification method. 'Wild' females were induced to lay eggs and the progeny reared as individual families. Resulting adults were cross-mated to a laboratory colony strain of A. quadriannulatus originating from the Kruger National Park, South Africa. Hybrid progeny were obtained only from the colony female x Ethiopian male cross. This cross produced a female/male sex ratio of 0.48. Male offspring were sterile and ovarian polytene chromosomes from hybrid females showed typical asynapsis as expected in interspecific crosses within the A. gambiae complex. The X chromosomes, although apparently having homosequential banding patterns, were usually totally asynapsed. All autosomes were homosequential. The lack of inversion heterozygotes, in both the wild and hybrid samples, may simply be a reflection of the small sample size. Until such time as the Ethiopian species can be formally described and assigned a scientific name, it is provisionally designated Anopheles quadriannulatus species B because of its close similarity to this species.