In order to determine whether the digital plethysmogram (PTG) can be used as an index of ageing or not, the PTG was recorded in 89 males and 110 females in a pilot study. Of the parameters which were calculated from the PTG, up-stroke time corrected by pulse rate (SXp time) showed the strongest correlation with age. The PTG was recorded in 1066 males and 761 females. There was a significant correlation between age and SXp time in both sexes. The change of SXp time with age in the younger age group was more rapid than in the old age group. From these results, SXp time of the PTG can be used as an index of ageing, especially in the young to middle-aged group.