The aim of this in situ study was to test the effect of toothbrush abrasion on enamel previously exposed to a standardized artifical erosive agent. To generate moderate erosive lesions, slabs of the buccal surface of human premolars were immersed in a solution of citric acid for 3 min. Then they were attached to intraoral appliances and each one was exposed for 0 min (= toothbrushing immediately after intraoral exposure), 30 or 60 min to the oral milieu of 1 of 7 female subjects with a mean age of 22 years. Immediately thereafter the volunteers brushed the slabs for 30 s with toothpaste using their preferred brushing technique. For each test person the secretion rate of resting and paraffin–stimulated saliva, buffering capacity and pH were measured. The following mean losses of substance at the surface were registered: 0.258±0.141 μm (toothbrushing immediately after intraoral exposure), 0.224±0.087 μm (toothbrushing after intraoral exposure of 30 min) and 0.195±0.075 μm (toothbrushing after intraoral exposure of 60 min). Toothbrush abrasion in situ was significantly lower after 60–min exposure to the oral environment than after 0–min (p<0.001). Also, the 30– and 60–min values were significantly different from each other (p<0.001). Multiple linear regression analyses revealed that in this model toothbrush abrasion was associated with the intraoral exposure to saliva (p = 0.026), the severity of the erosive attack (p<0.001) and the secretion rate of resting saliva (p = 0.029). If no other preventive measures are taken we suggest that individuals at risk for erosive tooth wear wait at least 1 h before brushing their teeth after consuming erosive foodstuffs or beverages.