Clinical research on probiotics presents challenging issues for researchers, regulators, and funding agencies, and these issues become more complex when United States federally funded research is conducted outside the United States. Here, we describe the design and results of a Phase I safety study of Lactobacillus reuteri DSM 17938 conducted as a community-based trial under the Food and Drug Administration Investigative New Drug (FDA IND) program in a small town in the Peruvian Amazon. Forty-five healthy adults 18 to 65 years of age were randomized in a 2:1 ratio to receive either Lactobacillus reuteri 108 organisms once daily for 5 days or an identical appearing placebo. Results showed no evidence of invasive infection resulting from probiotic administration and no differences between groups. Although we encountered several challenges in conducting an FDA-approved safety trial in this setting, the rigorously collected contextually relevant data will be very valuable to support later Phase II/III studies of L. reuteri for use in similar settings. Copyright © 2014 by The American Society of Tropical Medicine and Hygiene.