ABSTRACT.1There is a narrow hybrid zone between two chromosomal races of the grasshopperPodisma pedestris(L.) in the French Alps.2There are no gross differences in habitat across the zone, and a multivariate analysis of the vegetation composition detected no significant transition either.3The hatch and development rates ofPodismain hybrid populations were lower than those found in matched habitat types outside the zone.4The simplest explanation for the persistence of the parapatric distribution of the two races is that hybrid disadvantage is maintaining a tension zone between them.