Chemotaxis of diabetic monocytes was studied. The use of 0.25 x 10(6) monocytes, 20% Zymosan activated serum and incubation at 37℃ for 90 minutes were found to be the optimal assay conditions for the Boyden chamber method using a nuclepore filter. Under these conditions, monocyte chemotaxis was tested in 48 diabetics and 27 normal controls. The results were as follows: 1) Diabetics had low monocyte chemotaxis, especially in aged patients. The normal controls showed no difference with aging. 2) Poorly controlled diabetics showed significantly lower chemotaxis than both normal controls(P<0.005) and good controlled diabetics(P<0.05). The mean values were 40.1±32.4, 71.3±29.9 and 61.4±36.2 monocytes/HPF, respectively. 3) There was no difference in monocyte chemotaxis between diabetic groups treated with diet alone, oral agents or insulin. 4) Six of nine poorly controlled diabetics showed increased monocyte chemotaxis after being good controlled with insulin.