Altered concentrations of bile acid (BA) in the colon can cause diarrhea or constipation. More than 25% of patients with irritable bowel syndrome with diarrhea or chronic diarrhea in Western countries have BA malabsorption (BAM). As BAM is increasingly recognized, proper diagnostic methods are needed to help direct the most effective course of treatment for the chronic bowel dysfunction. We review the methodologies, advantages, and disadvantages of tools that directly measure BAM: the 14C-glycocholate breath and stool test, the 75selenium homotaurocholic acid test (SeHCAT), and measurements of 7 α-hydroxy-4-cholesten-3-one (C4) and fecal BAs. The 14C-glycocholate test is laborious and no longer widely used. The 75SeHCAT has been validated but is not available in the United States. Measurement of serum C4 is a simple and accurate method that can be used for most patients but requires further clinical validation. Assays to quantify fecal BA (total and individual levels) are technically cumbersome and not widely available. Regrettably, none of these tests are routinely available in the United States; assessment of the therapeutic effects of a BA binder is used as a surrogate for diagnosis of BAM. Recent data indicate the advantages to studying fecal excretion of individual BAs and their role in BAM; these could support the use of the fecal BA assay, compared with other tests. Measurement of fecal BA levels could become a routine addition to the measurement of fecal fat in patients with unexplained diarrhea. Availability ultimately determines whether the C4, SeHCAT, or fecal BA test is used; more widespread availability of such tests would enhance clinical management of these patients.