Beagle dogs were treated with 0.1 % aqueous solution of benzethonium chloride or with water for 27 weeks and for an additional three weeks to ascertain whether or not the plaque inhibiting effect of BTC was altered because of initial long‐term treatment. The results of this study show 0.1 % BTC significantly reduced plaque and gingivitis in beagles for 27 weeks, This plaque inhibitory effect of BTC was maintained in the subsequent three weeks, suggesting that its initial 27 weeks usage did not result in a change of “oral flora” that affected its eff