Species compositions of populations along a transect across a narrow hybrid zone between Ranidella insignifera‡ and R. pseudinsignifera‡ were determined using diagnostic enzyme loci and multivariate analysis of skeletal parameters. These were compared with subjective assessments of male mating call choruses in the same populations. The three independent characters all demonstrated a sharp transition from one species to the other over a distance of 2·4 km indicating some barrier to gene flow between the species beyond this narrow hybrid zone. It is suggested that the contact between the two species is a relatively old and stable one. Possible explanations for the maintenance of the 480 km parapatric boundary between the two species are examined.