This is a phase IIa, randomized, placebo-controlled, single-blinded superiority treatment study 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. Primary objectives are 1) to compare the proportion of subjects with stools positive by rapid 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 and 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 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 cysts or trophozoites by microscopic exam or negative antigen detection) at 14 and 28 days, and 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. 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 cysts or trophozoites by microscopic exam or negative antigen detection) 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. The length of this study is set for 3.5 years; subject participation is 7 days treatment for amebiasis and 5 days for giardiasis with follow-up until day 28.