Rhesus monkeys from the closed Cayo Santiago colony of the University of Puerto Rico demonstrate elevated (> or = 22 mm Hg) intraocular pressure in a pattern which significantly favours certain maternal lineage groupings. The colony had remained genetically pure since 1938. Of nine matriarchal lineages (matrilines) examined, two had an incidence of ocular hypertension of more than 40% and six of more than 10%. Information on 18 matrilines is currently located in the colony data base which identifies each individual and its vital statistics. In 1990, six animals were moved to the laboratory in Florida. Among those from a low incidence matriline, we found abnormal optic nerve cups, pallor, reduced function of (mainly peripheral) fields, progression and loss of optic nerve axons in the presence of ocular hypertension. In another individual where the cup/disc ratio for the right eye was 0.7 and left eye 0.4 and outflow facility was normal, we excluded all other causes of optic nerve atrophy, and low tension glaucoma was diagnosed. This female was from a matriline with a low incidence of ocular hypertension. Relatively rapid aging (3-4 years/human year) monkeys with ocular hypertension and familial clustering produce a near ideal glaucoma research model.