Objectives:Many a times in clinical periodontology, the decision whether to prescribe prophylactic antibiotics or not, is perplexing.The present study was conducted to compare the bacteremias induced after periodontal flap surgeries with and without prophylactic antibiotics.Materials and Methods:The occurrence of postoperative bacteremia following periodontal flap surgery was studied in 30 patients. On these patients, 30 quadrant wise flap surgeries were carried out without any preoperative prophylactic antibiotics and 30 surgeries carried out after prophylactic administration of amoxycillin preoperatively. A blood sample was taken from each patient at the time of maximum surgical trauma and was cultured for micro-organisms and antibiotic sensitivity.Results:18 out of 60 blood samples were positive for micro-organisms. There was a significant reduction in post operative bacteremia after amoxycillin prophylaxis (x2 - 7.96 with P<0.01) as post operative bacteremia was found in 14 of the non medicated patients as compared to only 4 of the pre medicated patients. The micro-organisms encountered in the study are as follows:- 1) Staphylococcus albus coagulase negative, 2) Klebsiella, 3) Psedomonas aerugenosa, 4) Streptococcus viridans, 5) Alpha hemolytic streptococcus, 6) Neisseria catarrhalisConclusion:On the basis of the study, it is concluded that the incidence of postoperative bacteremia following periodontal flap surgery is not as high as previously reported. The clinical results show that Amoxicillin is highly effective in reducing postoperative bacteremia in periodontal flap surgery and thus in preventing the possible sequelae (Infective Endocarditis and other systemic maladies) in susceptible patients. However, cefotaxime and cephalexin may prove to be more effective in preventing the same.