To determine the effect of the smoking experience on relative blood flow in gingiva and to compare this to skin. A laser Doppler flowmeter was used to record relative blood flow to healthy gingiva and to forehead skin in smokers and non-smoking controls. Smoking status was verified by quantitative analysis of serum cotinine. Continuous measurements were made over sequential periods with the subject at rest, during a sham smoking exercise, during smoking of a standard research cigarette (2R1, University of Kentucky) for 5 min and throughout a subsequent recovery period. Non-smoking controls sham smoked during the equivalent 5 minute smoking period. No significant differences with respect to the proportional changes of relative gingival blood flow between time points were observed between the groups. However, between-group comparisons of relative blood flow revealed a significant increase in the relative blood flow to the forehead skin of light smokers (serum cotinine < or =60 ng/ml; n=6), when compared to heavy smokers (serum cotinine > or = 100 ng/ml; n=9) or to non-smokers (serum cotinine < or = 10 ng/ml; n=6), 2 min following the smoking experience (p = 0.007). The results do not seem to support the theory that tobacco smoking causes localised vasoconstriction in the periodontal tissues in humans. These data show that smoking causes an acute increase in relative blood flow in forehead skin in light smokers compared to heavy smokers, suggesting a potential induction of tolerance in regular users of tobacco.