Numerous writers have found the origin of the Ayrshire breed of cattle an intriguing study, and although many have tried to throw light on the subject, the historic origin of the progenitors of the breed is still somewhat obscure. 1. Breed evolution was influenced by the introduction of imported stocks. 2. Shows have affected the development of the breed - beneficially and adversely, according to the standards set by the judges. 3. Homozygosity in the breed has been attained by selection, with but little recourse to inbreeding. This does not apply to the vessel bred type. 4. No sex difference in respect of inbreeding has been noted. 5. No relationship has been demonstrated between inbreeding and productivity. There is also no conclusive evidence that inbreeding has had a detrimental effect on high milk production. 6. One herd - Drumjoan - and one sire - Drumjoan Hover -a -Blink - have had an outstanding influence on the breed, but this influence came through the fact that he sired bulls of good conformation. Such inbreeding as took place to him was largely incidental because he had so many sons of good show type. 7. The level of inbreeding amongst vessel bred type is significantly higher than that of the milk type.