Boa constrictor occidentalis, the only subspecies of the genus Boa present in Argentina, is endangered because of the strong hunting pressure due to the skin and pet-shop trade and the destruction and fragmentation of its habitat. We estimated levels of protein polymorphism and determined the degree of genetic differentiation between two populations of B. c. occidentalis in Córdoba province, Argentina. We obtained blood samples from 93 specimens in two sampling sites 200 km apart. A total of 17 proteins affording information on 25 presumptive loci were studied by gel electrophoresis techniques. Only four loci were polymorphic: 6-Pgdh-1, Cat-1, Ldh and Hp. The mean heterozygosity per locus was low (0.06 and 0.07). Life history and ecological traits of this snake may explain the low levels of polymorphism found. No evidence of inbreeding was detected. The average genetic differentiation between the two sampled areas was not significant ( = 0.004). These results would indicate a relatively recent fragmentation of an original gene pool.