Synthetic thymosin beta 4 (Tbeta4) may have a potential use in promoting myocardial cell survival during acute myocardial infarction. Four cohorts, with 10 healthy subjects each, were given a single intravenous dose of placebo or synthetic Tbeta4. Cohorts received ascending doses of either 42, 140, 420, or 1260 mg. Following safety review, subjects were given the same dose regimen daily for 14 days. Safety evaluations, incidence of Treatment-Emergent Adverse Events, and pharmacokinetic parameters were evaluated. Adverse events were infrequent, and mild or moderate in intensity. There were no dose limiting toxicities or serious adverse events. Pharmacokinetic profile for single dose showed a dose proportional response, and an increasing half-life with increasing dose. Synthetic Tbeta4 given intravenously as a single dose or in multiple daily doses for 14 days over a dose range of 42-1260 mg was well tolerated with no evidence of dose limiting toxicity. Further development for use in cardiac ischemia should be considered.