Abstract
The origin of 3 inbred albino rat strains, AS, AS2 and OH, is traced from the same random-bred albino colony. Both the AS and OR strains are hypertensive, while the AS2 strain and the random-bred albino rats are normotensive. The OH breeders have been routinely selected for high blood pressure, while AS breeders are selected for intrastrain histocompatibility. It is highly likely that AS originated as a subline of OR in 1960. The AS and OR strains have been maintained separately since 1960, and the blood pressure is currently higher in OR than in AS.