The test is similar to the one used to determine when a driver has had too much to drink.
In a new study from Italy researchers tested 37 people who had colorectal cancer and 41 people without cancer.
Researchers were able to identify cancer patients with 75 percent accuracy by analyzing breath samples.
Doctors say the technique of breath sampling is still in the early phase of development, but it could be a reality within five years.
The study is published online in the British Journal of Surgery.