A total of 816 rabbits, belonging to breeds presently bred in Spain (Spanish Common, Spanish Giant, Butterfly, Lyone de Bourgogne, New Zealand White, Californian and a hybrid line obtained from crosses between selected individuals of the latter two), were tested using nine blood electrophoretic markers: Hb, Ak, Co, Tf, Es-l, Es-2, Es-3, Ada and Pgd. The latter five proteins were found polymorphic, each being controlled by one locus and showing autosomal co-dominant Mendelian inheritance. Three of these loci (Es-1, Es-2 and Pgd) have two alleles, and the remaining two (Es-3 and Ada) have three alleles. These polymorphic loci were used to study the population structure and breed similarities genetically.Gene frequencies for Es-1, Es-3 and Ada clearly differed amongst populations. Intra-breed variation was found for Es-3 in the Spanish Common breed. Lack of Hardy-Weinberg equilibrium was only found for Es-2 in most populations. Average inbreeding coefficients were not significantly different from zero, except in Spanish Giants (f = O· 09) and New Zealand Whites (f = -0·04). To estimate the genetic variability the average degree of heterozygosity was calculated and gave values of 0·40-0·56 for Es-1, Ada or Es-3, 0,82-0,84 for Es-2, due to an excess of heterozygotes, and 0,08-0,10