Sanitation is the greatest medical advance since 1840, according to voters in a poll on the medical journal BMJ's web site.

The runners-up: antibiotics and anesthesia, says BMJ (formerly the British Medical Journal).

Last year, BMJ invited readers to submit nominations for the top medical breakthrough since 1840, the year the journal was launched.

BMJ then posted 15 nominations and invited people to vote on its web site between Jan. 5 and Jan. 14, 2007.

Votes poured in from more than 11,000 people (mainly doctors) in countries including Australia, Bulgaria, Canada, Germany, India, Italy, Spain, U.K., and the U.S.

Here, in order, are the results:

1. Sanitation: 1,795 votes.The importance of clean drinking water and waste disposal was recognized in the late 1800s, as diseases began to be linked to impure water. However, the World Health Organization says there is still a long way to go. More than 1.1 billion people now lack access to drinking water from an improved source; 2.6 billion do not have basic sanitation.

2. Antibiotics: 1,642 votes.Alexander Fleming, a British bacteriologist, discovered penicillin in 1928 by accident when he sloppily left a Petri dish of bacteria unwashed in his lab. He found a substance (later named penicillin) growing on it that killed the bugs, and modern-day antibiotics got its start. Fleming shared the Nobel Prize in 1945 for the discovery.

3. Anesthesia: 1,574 votes.In 1846, a Boston dentist used ether during surgery, putting an end to much of the pain of operations. Since then, general anesthesia has become a mainstay.

4. Vaccines: 1,337 votes.Vaccines have helped prevent a variety of diseases -- including polio, whooping cough, and measles. The first was Edward Jenner's smallpox vaccine, in 1796.

5. Discovery of DNA structure: 1,000 votes.Scientists James Watson and Francis Crick presented the structure of the DNA helix, the molecule responsible for carrying genetic information from one generation to the next, in 1953. It earned them the Nobel Prize in 1962.

6. Germ theory: 843 votes.In the late 1800s, Louis Pasteur was the first to suggest that disease is caused by exposure to microorganisms. Others furthered the theory, showing that specific diseases are caused by specific "bugs."

7. Oral contraceptive pill: 842 votes. The pill arrived on the U.S. market in 1960. For women who use it correctly, oral contraception can be up to 99% effective at preventing pregnancy.

8. Evidence-based medicine: 636 votes.As the name suggests, evidence-based medicine involves making use of the current best evidence (such as research), combined with a patient's values and a doctor's clinical experience, to make decisions about patient care. The term was coined in the early '90s and the concept has been evolving ever since.

9. Medical imaging: 471 votes.The X-ray was accidentally discovered in 1895. Since then, the field has expanded, giving us computed tomography (CT scans), positron emission (PET scans), magnetic resonance imaging (MRIs), and ultrasound.

10. Computers: 405 votes. From medical records to insurance, to making sure your new medication isn't going to clash with an existing one, computers are now considered as important as their stethoscopes by some doctors. They've been in use in medicine since the early 1960s. Doctors can access information on new drugs and interactions, new medical studies, and clinical trials, and keep patient records stored at their fingertips.

11. Oral rehydration therapy: 308 votes.This therapy involves giving fluids by mouth to replace losses by the body. It was first reported in 1964; now it's a mainstay of treatment in patients with cholera, acute diarrhea, and other conditions.

12. Risks of smoking: 183 votes.The first report of the connection between smoking and lung cancer was published in BMJ in 1950. Even so, tobacco use still kills an estimated 440,000 Americans each year.

13. Immunology: 182 votes.The history of immunology is traced to 1798, when Edward Jenner found that people could be immunized against the disease smallpox. Numerous other immunology discoveries followed, leading to a greater understanding of such things as allergies and antibodies.

14. Chlorpromazine: 73 votes.Discovered in 1952, chlorpromazine (Thorazine) was the first antipsychotic medication. It was used to treat psychotic disorders and their symptoms, such as hallucinations, hostility, and delusions. Its development brought new understanding of the biological basis for mental illness, and some say it provided more humane management.

15. Tissue culture: 50 votes.Tissue culture (keeping tissue alive and growing it in a culture medium for research or other purposes) was "discovered" in 1907; but it took until the 1950s for it to become an important tool for clinical investigation.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: News release, BMJ. WebMD Medical News: "What's the Greatest Medical Advance?"