Genetic relationships among 37 European cattle breeds were investigated using blood group and serum protein polymorphisms. The 18 859 animals included in the study represented a random sample from pedigree populations in the UK. Within‐breed variation was estimated by average heterozygosity and number of alleles observed, and breed relationships were evaluated by genetic distance. Standard errors of the heterozygosity, number of alleles and genetic distance were obtained by bootstrapping. The significance of breed differences was tested using an exact test of differentiation. French, Italian and Channel Island breeds were found to have generally higher heterozygosities and a greater number of alleles than breeds from mainland Britain and North Europe. Genetic distances ranged between 0·011 (±0·005) and 0·309 (±0·071). Two major breed groups were identified; a group of French, Italian and Channel Island breeds together with the Simmental and Gelbvieh, and a second group consisting of the mainland British and North European breeds. The exact test of breed differentiation showed all breeds to be significantly different from one another (P < 0·0001). Overall relationships among breeds reflected their geographical origin and common ancestry rather than the agricultural use for which the breeds have been selected.