dr. pamela ling says without regulation, it's hard for users to know exactly what's in e-cigarettes. >> they think, well, this is just nicotine and harmless water vapor, and what's the big deal? actually, we know that nicotine is a highly addictive drug, and we don't know what the combination of chemicals in the e-cigarettes does to the body. >> reporter: but at xl parts in ft. worth where employees are allowed to vap on the job, they're convinced they're healthier.until i tried this. and now i don't smoke any more. i didn't think i'd ever say that. >> reporter: chris putnam says he's more productive too. >> probably it takes on average ten minutes to smoke a cigarette. if i do that eight, nine times a day -- >> reporter: which you used to do? >> which i used to do, yeah. that's pretty much an hour of time i'm not working. >> reporter: with sales expected to top $1 billion this year, it's no surprise all three big tobacco companies are now investing in e-cigarettes, looking to replenish their shrinking customer base by jumping on a growing trend. kate snow, nbc news, ft. worth, texas. >>> an