Abstract
Fecal samples from twelve subjects who received liquid formula diet for 47 days or longer were analyzed for mutagens with the fluctuation test for weak mutagens using Salmonella typhimurium TA 100 as a tester strain. The purpose was to establish the variation of fecal mutagens among subjects on identical diets and the variation within a subject when on a constant diet. It was found that there was significant inter‐subject variability which did not disappear even after 72 days of rigorously controlled diet. There was no significant change, within a subject, of fecal mutagenicity throughout the diet period. It appears that long‐term habits (dietary or otherwise) or, perhaps, genetic traits are major factors influencing fecal mutagenicity.