(FORTUNE Magazine) – Remarkably, the Pap smear -- the most widely used cancer-screening test for women -- has not changed since 1950, when doctors started using it routinely to check for cervical cancer. Lab technicians still analyze specimens one at a time under a microscope. They must spot subtle changes among as many as 100,000 cells on a single slide; often cells are clumped together and obscured by blood and tissue, making the process even more difficult. Some 50 million American women get a Pap test each year. Medical experts consider it one of the great success stories in cancer prevention because it catches precancerous abnormalities long before they have a chance to turn deadly. Cervical cancer grows slowly, often taking more than ten years to develop. But Pap tests have a high failure rate. Labs miss abnormalities in as many as one in five cases where they exist, giving the test a ''false negative'' rate of about 20%. That's why doctors recommend annual screenings: They figure problems that aren't found one year will be caught the next. Cytyc Corp., a biotech startup company in Marlborough, Massachusetts, has developed an automated procedure that increases the odds of finding abnormalities as soon as they develop. The process, called ThinPrep, enables doctors to collect many more cells than with a conventional Pap test and cleans them up so that the specimen is far easier to analyze. The procedure works this way: Instead of smearing a specimen of vaginal secretions directly onto a slide, the doctor rinses the swab used to collect the cells in a vial of preservative solution. The solution captures almost all the cells; in a conventional smear, as many as 95% get tossed into the garbage with the swab. At the lab, a technician inserts the vial into a processing machine the size ) of a microwave. It sucks the cell-laden fluid through a filter that breaks up mucus and clumps of cells and removes debris. With a puff of air, the machine then deposits a representative sample of 50,000 clean cells in a thin, uniform layer on a slide for the technician to read. A Food and Drug Administration panel last summer unanimously recommended that ThinPrep be approved for use in Pap tests; Cytyc expects approval by the full agency this year. Labs already use the process to screen for cancer cells in urine, spinal and chest fluids, and sputum. A recent issue of the American Journal of Clinical Pathology should stimulate demand. It reports that in a study at five large labs and health centers around the country, Cytyc's process led to a 13% increase in disease detection vs. the conventional Pap smear, and produced false negatives in only one-fourth as many cases. Says Dr. David Kaminsky, president of the American Society of Cytology, who oversaw the use of ThinPrep in some 5,000 cases in California last year: ''You get a richer harvest of cells that are better preserved.'' At $30,000 for the processor and about $2 per test for vials, preservative solution, and filters, ThinPrep isn't cheap. But it could bring down the total cost of Pap smears by cutting the number of cases, now as many as one in ten, in which a second smear is needed because the first was too hard to read. Cleaner specimens will also ease the lot of lab technicians, who examine an average of 2.5 million cells a day. Their high burnout rate has forced labs to raise starting salaries to about $30,000. That, along with increased federal regulation, has tripled the going rate for a Pap smear to more than $30 in many cities.