To describe variation in size of offspring across a hybrid zone between the myobatrachine frogs Geocrinia laevis and Geocrinia victoriana, the sizes of tadpoles hatching from egg masses collected in the field were measured. Hatchling size was strongly correlated with diameter of the blastula or gastrula (referred to here as "egg size"). Geocrinia victoriana had bigger offspring than G. laevis. Hybrids were generally intermediate between the two parental species in offspring size. However, the variation in size across the hybrid zone did not show a smooth cline or a distinct step coinciding with any of the sharp transitions found for behavioural or genetic characters. Variation within hybrid populations was not greater than in "pure" samples of the two species; these data correspond to findings of other studies which showed that this contact between G. laevis and G. victoriana is a "true hybrid zone" with panmictic local populations, not an overlap of the two species.