Background: Safety, pharmacokinetics and pharmacodynamics of BMS-986166, a novel sphingosine-1-phosphate receptor 1 modulator, were assessed.Research design and methods: Two double-blind, placebo-controlled, randomized Phase l studies were conducted in healthy participants. In the single ascending dose study (N = 70), BMS-986166 was administered as a single dose, upwardly titrated daily doses or a single dose in participants who were fed, fasted or administered famotidine. In the multiple ascending dose study (N = 32), BMS-986166 was administered daily for 28 days. Safety, pharmacokinetics and pharmacodynamics (absolute lymphocyte count [ALC]) were assessed.Results: BMS-986166 was generally well tolerated; treatment-related adverse events were mild. Dose-related, clinically insignificant reductions in time-matched heart rate were recorded versus placebo. Pharmacokinetics were linear and stationary with approximately dose-related increases in blood exposure of BMS-986166. Decreases in ALC percent change from baseline with multiple doses of BMS-986166 versus placebo were dose-related. Between Day 0 and 35, median nadir lymphocyte reductions were 53.7%, 75.9% and 81.9% with 0.25-, 0.75- and 1.5-mg BMS-986166 doses. ALC recovery began 14, 14-21 and 7 days after last dose of 0.25, 0.75 and 1.5 mg.Conclusions: BMS-986166 was generally well tolerated in this population and warrants further investigation.Trial registration: ClinicalTrials.gov: NCT02790125, NCT03038711.