Impact by pulsed laser irradiations from an Nd:YAG laser on the marine biofilm-forming bacterium Pseudoalteromonas carrageenovora has been studied using a flow cytometric system. The biofilm-forming bacteria in the planktonic state have been irradiated while flowing, and the mortality and bacterial attachment have been determined by exposing TiN coupons in the system. Coupons suspended in the non-irradiated bacterial flow were treated as the control. The fluence used in the study was 0.1 J/cm(2). Three flow rates (14, 28, and 42 cm/min) and two exposure durations (15 and 30 min) were tested. The results showed the increase in bacterial mortality with the decrease in flow rate. The maximum mortality of 27.5% was observed when the flow rate was 14 cm/min. The bacterial attachment increased with the increase in flow rate and exposure duration. The area of bacterial attachment on the experimental coupons exposed to the irradiated sample was significantly lesser than that for the nonirradiated sample. The results thus show in a flowing system, low power pulsed laser irradiations could reduce the bacterial attachment even though it did not cause significant mortality. (C) 2003 Wiley Periodicals, Inc.