The effects of altitude on a series of ocular functions were studied on seven expedition members, all women aged 23-53 years, during the first ascent of the 6798-m peak Brigupanth in the Indian Himalayas. The only consistent change was a decrease in convergence amplitude. The amplitude of accommodation remained stable among the younger climbers, but decreased markedly among the older ones as higher altitudes were reached. There also appeared to be a lessened vascular reactivity to the hypoxia of altitude in the older members. Stereoscopic vision was unimpaired at all altitudes tested and extra-ocular muscle balance remained unaffected in all but two members who had an increase in their baseline phorias. Two of the summit climbers developed retinal hemorrhages. There was an average weight loss of 5.4 kg during the climb, but general health was good. Symptoms of acute mountain sickness were noted infrequently, and there were only moderate changes in the menstrual cycle.