Laser Doppler flowmetry was used in 14 subjects to investigate the effect of sodium lauryl sulfate (SLS) on gingival microcirculation. SLS, the most widely used detergent in toothpastes, exhibits a denaturing property, increases oral mucosal permeability and may cause epithelial desquamation of oral soft tissues. Gingival blood flow (GBF) was measured bilaterally 3 mm above the gingival margin, between the central and lateral maxillary incisors, before and after application of 1.5% SLS for 90 s to the gingiva on one side. The contralateral side served as a control with water application only. Relative changes in GBF were measured for 15 min on both sides. SLS increased the median GBF significantly between the 2nd and 10th min with a peak at 8 min, whereafter the flow decreased towards baseline. On the contralateral side, GBF initially declined before returning to baseline. 10 subjects felt a burning pain from the gingiva after SLS application and GBF increased in all of them. SLS increased the relative gingival blood flow presumably due to its penetrating and irritative properties, which resulted in vasodilatation. Laser Doppler flowmetry may be a useful non-invasive method for intraoral testing of different agents meant for oral use.