Object To observe the characteristic values of photoplethysmogram on the 5 diseased skin colour (reduess, paleness, yellow, blue, black of the skin). Methods To examine and analyse the photoplethysmogram of the cheeks of 447 pathents and 40 normal adults with “BC 4” photoplethysmograph. Results The 5 diseaed skin colour differs greatly from the normal skin colour (be ruddy cheeked) in the values of Hb/Tab, T w/Tag, Tab/Tag,He/Hb,[Tae Tab]/Tag(all P< 0 05 or P< 0 01). There are much different in the aforementioned valueses on the 5 diseased sk...