At each of your clinic visits, your blood pressure will be taken and you will be asked to blow air through a carbon monoxide (CO) measuring device. CO is a gas that is found in higher levels among cigarette smokers. At several visits you will be asked to provide a saliva sample to check for cotinine, a chemical produced by the breakdown of nicotine during smoking. You will be asked to give a saliva sample in a collection tube. Like the CO test, this test will help researchers measure how much you are smoking.