This is a phase IIa, randomized, placebo-controlled, single-blinded superiority treatment study in males and non-pregnant females, 18 to 65 years of age who are in good health. This study is designed to compare placebo to once daily doses of 6mg auranofin for adults with amebiasis or giardiasis. A sample size of 68 subjects enrolled with amebiasis (34 per arm) and 68 with giardiasis (34 per arm); Power based on 60 subjects with amebiasis and 60 with giardiasis completing the study. Eligible subjects will be randomly assigned to a treatment group with auranofin (6 mg orally once daily for 5 days for giardiasis or 7 days for amebiasis) compared to a placebo group receiving similar but not identical placebo capsules. Projected duration of subject participation will be approximately 30 days of face to face visits, including the pre-enrollment screening period of up to 4 days. It is anticipated that it will take approximately 3.5 years to finish the study. Primary objectives are: 1) to compare the proportion of subjects with stools positive by rapid Enzyme Immunoassay (EIA) and positive antigen detection EIA for E. histolytica at enrollment with resolution of diarrhea (less than 3 loose stools/24 hrs) by Day 7 for E. histolytica infections. 2) to compare the proportion of subjects with stools positive by rapid EIA and positive antigen detection EIA for Giardia at enrollment with resolution of diarrhea (less than 3 loose stools/24 hrs) by Day 5 for Giardia infections. Secondary objectives for E. histolytica infections are: 1) to compare the proportion of subjects with stools positive by rapid EIA and positive antigen detection EIA for E. histolytica and trophozoites on smear at enrollment with parasitological response (no detection of trophozoites of E. histolytica on microscopic exam) by Day 7; 2) to compare the proportion of subjects with stools positive rapid EIA and positive antigen detection EIA for E. histolytica and trophozoites on smear at enrollment with parasitological response (no detection of trophozoites on microscopic exam or negative antigen detection) by Days 3 and 5; 3) to compare the rate of decrease of trophozoites/cyst load by Quantitative Polymerase Chain Reaction (qPCR) in stools by Days 3, 5, and 7; 4) to compare the proportion of subjects with negative stool antigen tests by days 3, 5, 7, and 14; 5) to compare the proportion of subjects with sustained cure (no detection of trophozoites by microscopic exam) at 14 and 28 days; 6) to compare the proportion of subjects with relapse (same strain) or re-infection (new strain) with positive stools at 14 and 28 days by genotyping the initial vs. subsequent strain; 7) to compare the time to resolution of diarrhea (less than 3 loose stools/24 hours). Secondary objectives for Giardia infections are: 1) to compare the proportion of subjects with parasitological response (no detection of trophozoites on microscopic exam ) on Day 3, and 5; 2) to compare the rate of decrease of trophozoites/cyst load by qPCR in stools by Days 3 and 5; 3) to compare the proportion of subjects with negative stool antigens by days 3 and 5; 4) to compare the proportion of subjects with sustained cure (no detection of trophozoites by microscopic exam) at 14 and 28 days; 5) to compare the proportion of subjects with relapse (same strain) or re-infection (new strain) with positive stools at 14 and 28 days by genotyping the initial vs. subsequent strain; 6) to compare the time to resolution of diarrhea (less than 3 loose stools/24 hours).