The purpose of this study was to evaluate the effect of probe motion on laser probe temperature in various blood flow conditions. Laser probe temperatures were measured in an in vitro blood circulation model consisting of 3.2 nm-diameter plastic tubes. A 2.0 mm-diameter metal probe attached to a 300 microns optical quartz fiber was coupled to an argon laser. Continuous wave 4 watts and 8 watts of laser power were delivered to the fiber tip corresponding to a 6.7 +/- 0.5 and 13.2 +/- 0.7 watts power setting at the laser generator. The laser probe was either moved with constant velocity or kept stationary. A thermocouple inserted in the lateral portion of the probe was used to record probe temperatures. Probe temperature changes were found with the variation of laser power, probe velocity, blood flow, and duration of laser exposure. Probe motion significantly reduced probe temperatures. After 10 seconds of 4 watts laser power the probe temperature in stagnant blood decreased from 303 +/- 18 degrees C to 113 +/- 17 degrees C (63%) by moving the probe with a velocity of 5 cm/sec. Blood flow rates of 170 ml/min further decreased the probe temperature from 113 +/- 17 degrees C to 50 +/- 8 degrees C (56%). At 8 watts of laser power a probe temperature reduction from 591 +/- 25 degrees C to 534 +/- 36 degrees C (10%) due to 5 cm/sec probe velocity was noted. Probe temperatures were reduced to 130 +/- 30 degrees C (78%) under the combined influence of 5 cm/sec probe velocity and 170 ml/min blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)