Reciprocal allotriploid frogs, (T)TTI, (I)IIT, (T)TTH and (H)HHT, were produced from crossings between Rana tsushimensis from Tsushima, (T)TT, and Rana japonica from Ichinoseki, (I)II, and Hiroshima, (H)HH, by heat-shock treatment of fertilized eggs. Almost all the allotriploids developed normally and became males. In contrast, diploid hybrids between female R. tsushimensis and male R. japonica from Ichinoseki and the reciprocal diploid hybrids between R. japonica from Hiroshima and R. tsushimensis died of underdevelopment at the tadpole stage. However, diploid hybrids between female R. japonica from Ichinoseki and male R. tsushimensis could barely complete metamorphosis, although they died of infirmity within 1∿3 months after metamorphosis. Mature allotriploids were intermediate between the two parental species in external characters. They were more similar to the parental species giving two genomes than to the species giving one genome. A total of 65 mature male allotriploids including two kinds, (H)HHT and (T)TTH, between R. japonica from Hiroshima and R. tsushimensis and one kind, (I)IIT, between female R. japonica from Ichinoseki and male R. tsushimensis were completely sterile. On the other hand, 16 of 44 male allotriploids, (T)TTI, between female R. tsushimensis and male R. japonica from Ichinoseki were fertile. The spermatogenesis in these allotriploids was completely or partially normal. The other 28 male allotriploids, (T)TTI, were sterile. A total of 419 offspring were produced from seven of the above 16 male allotriploids by backcrossing with female R. tsushimensis. They were all diploids and of the R. tsushimensis type in external characters. Most of them (96.9%) were females. They showed the same electrophoretic patterns as those of R. tsushimensis at 14 loci of enzymes and blood proteins. These findings seemed to indicate that some of the male allotriploids reproduce by hybridogenesis, in which the R. japonica genome was eliminated during spermatogenesis.