A fecal transplant is exactly what it sounds like: To treat certain gut disorders, doctors transfer stool from a healthy donor to a sick patient.

Just a few years ago, only a few doctors turned to fecal transplants, typically as a last resort. But in randomized trials, the procedure has proved remarkably effective against potentially fatal infections of bacteria known as Clostridium difficile.

The evidence has overwhelmed any squeamishness that physicians might have felt. “We’re doing this treatment almost weekly,” said Dr. Harry Sokol, a gastroenterologist at Saint-Antoine Hospital AP-HP in Paris.

Now scientists are testing fecal transplants against such diseases as ulcerative colitis, and even obesity and diabetes. A batch of new companies, well funded with venture capital, hope to commercialize the research.