Objective:To observe the relationship between the fingernail colour and the photoplethysmogram. Methods:To examine the photoplethysmogram of the 160 cases of fingernail of 4 groups (the moist red, the light white, the deep red and the purplish blue) with “BC-4” photoplethysmograph, meanwhile observed microcirculation of the nailfold. Results:To compare the 4 groups, the value of Tab/Tag increased and the it of [Tae-Tab]/Tag decreased in the light white grop,the value of 1/2[Hb+Hd]/Tae and [Tae-Tab]/Tag increased in the deep red grop; ...