Objective To analyze a population of cells on the right lower lateral of monocyte population in forward scatter/side scatter(FSC/SSC)(X-axis/Y-axis)scatterplot of peripheral blood leucocyte by flow cytometry(FCM)and its influencing factors.Methods The type of cells were identified based on cluster of differentiation antigen(CD)by FCM.The impact of temperature,hemolysin concentration,and incubation time was evaluated.Blood lipid tests were performed to observe the relation between them by statistical methods.Results (1) Phenotypo of this population of cells on the right lower lateral of monocytes in FSc/SSC scatterplot is CD+45 CD+13 CD+14 CD3- CD-19 ,which was the same as monocyte cells:(2)The monocytes in FSC/SSC scatterplot shifted to left side after using haemolysin;(3)The monocytes showed less resistance to antihemolysin in 37℃ than that in 220C:There were more monocytes shifting to left side with the increase of haemolysis time:(4)The swarming ratio of monocytes in patients (31.5%,40/126) Was higher than it in normal controls (5.1%,5/98)(x2=22.74,P<0.01);(5)The levels of total serum cholesterol(TC),triglyeride(TG),low density lipoprotein cholesterol(LDL-C), apoprotein B100(Apo B100) in patients with swarming monocytes were lower than that in the patients without swarming monocytes,(P<0.05).There was no statistical significance between the two groups with respect to levels of total bilirubin(TBIL),albumin(Alb),hish density lipoprotein cholesterol(HDL-C),apoprotein A I(Apo A I),lipoprotein(Lpa).Conclusions Peripheral blood monocytes can be divided in two groups in FSC/SSC scatterplot when analyzed with FCM.The presence of this population of cell Was related to resistance to hemolysin.It can be influenced by haemolysis time and incubation temperature.Therefore,the effect of swarming monocytes and abnormal cell membrane should be taken into consideration when the markers and function of monocytes are detected by FCM.