The corso imo is still a breed in development. The main differences I have found bewteen the two lines are: Temperment: I have found that both lines temps can very, I have seen extremely aggressive dogs, both dog and social. Timid dogs, and totally indifferent. Each corso is different Confirmation/Structure: In the past white on the toes was frowned upon. Now you can see corso with a full white chest, quarter white on the feet. The bite of the dogs vary as well. Scissors bite, reverse scissors, under shots as well. When I first got involved with the Corso I never saw any undershot dogs. The ones I did notice them on were the italian import. The setting of the eyes are a major difference I have noticed. Many imports have boxer/bulldog type eyes, almost pertruding. Size--is one of the biggest problems I have with the breed. My first Corso comes from old italian stock, she is what I call the old blooded corso. Many, Many foundation dogs linedbreed in her pedigree, e.g. Cocomo, Nero and so on. Throughout the years I have seen the dogs continaully lose size and bone mass. I have also noticed the loss of forehead mass as well. Working ability--is up in there. It will depend on temperment which varies widely within the breed. They are capable of doing most task if the right dog is selected. Basically the differences within the breed is due to human intervention with each group saying it ideal corso is the only one.