A total of 444 healthy eyes in 290 subjects of varying age were examined ultrasonically with a frequency of 6 MHz. In subjects under 20 years the structure of the vitreous body was acoustically homogeneous, and in those between 21 and 40 there was slight degeneration in 5% of the eyes. In the age group 41-50 the incidence of degeneration was 19%, in the group 51-60 63% and in that over 60 more than 80%. There was a clear increase in acoustically observable degeneration after the 40th year; nevertheless, in about 10% of those over 60 years an acoustically homogeneous vitreous body was observed. Ultrasonic observation can be used to supplement optical observations, and in the case of elderly patients is often the only way of obtaining information on the structure of the vitreous body.