Visual evoked responses (VERs) were elicited in 70 infants with postmenstrual ages between 30 and 39 weeks. On the basis of neurological and ultrasound examinations, 30 of the infants were classed as neurologically normal and 40 as abnormal: 26 of the latter had periventricular haemorrhage. Initially the VER consisted of a negative deflection only, and the appearance of a positive wave immediately preceding the negative deflection was taken to indicate maturation of the VER. Maturation was significantly delayed in the neurologically abnormal infants, and the delay was related to the degree of neurological insult. The visual acuity of 32 infants was estimated within seven days of the VER recording. There was a correlation of 79 per cent between the VER and the data for visual acuity.