T. spiralis DNA in feces of mice infected with 100 or 300 larvae was assayed by PCR. The sensitivity of PCR was 0.016 larvae in feces. No cross-reactivity was observed with the DNA of other intestinal helminths. T. spiralis DNA was detected in 100% (12/12) of the feces of infected mice at 3 hpi. Detection of fecal DNA might be useful for early diagnosis of Trichinella infection.