This prospective, randomized, double-blind, crossover study examined the effects of oral iron ingestion on fecal occult blood testing. One hundred healthy and asymptomatic volunteers collected stool samples after 2-wk courses of both oral iron (either ferrous sulfate or ferrous gluconate) and placebo, while following strict medicinal, dietary, and collection instructions. Each sample was tested by both the Hemoccult II and Hemoccult Sensa methods. Of the participants who completed this study (n = 78), there were no positive results for occult blood after iron ingestion when tested by either method. Only one participant displayed a positive result while taking the placebo, with this specimen considered contaminated by unexpected menses. From these findings, it can be concluded that oral iron supplementation does not cause false-positive results when the Hemoccult II or Hemoccult Sensa method is used for fecal occult blood testing.