The effects of carotid sinus massage in aged subjects with a high incidence of arteriosclerosis are described. In 71 men and 315 women tested, a slowing of more than 10 per cent of the heart rate was found in 25 per cent of the men and 19 per cent of the women, which is not of statistical significance in relation to sex. Only men showed a significant increase with age and the women had a significant preponderance of a right-sided response. The technique was found to be safe, although a review of reported side-effects suggests care is advisable and carotid compression must not occur. The findings are discussed in relation to those reported in younger subjects and in carotid sinus syndrome with syncope. The fact that men have an acquired increase in response in old age, which is not seen in women, may be a factor of importance in the explanation of why carotid sinus syncope is almost always seen in men. Carotid sinus sensitivity appears to diminish in old age and some of the ageing factors which might influence the carotid sinus reflex are examined.