Tbo-filgrastim is a recombinant human granulocyte colony-stimulating factor approved by the US Food and Drug Administration to reduce the duration of severe neutropenia in patients with nonmyeloid malignancies receiving myelosuppressive anticancer drugs associated with a clinically significant incidence of febrile neutropenia. We assessed the effect of tbo-filgrastim on cardiac conduction and repolarization in healthy subjects. A three-arm, parallel-group, active- and placebo-controlled, double-blind study randomized healthy adults to a single 5 μg/kg intravenous tbo-filgrastim infusion, a single intravenous placebo infusion, or a single 400 mg moxifloxacin oral dose. The primary end point was placebo-corrected time-matched change from baseline in QT interval corrected using a QT individual correction (QTcI) method. Secondary end points included heart rate, PR interval, QRS duration, change in electrocardiogram patterns, correlation between QTcI change from baseline (milliseconds) and tbo-filgrastim serum concentrations, and safety variables. A total of 145 subjects were enrolled (50 tbo-filgrastim, 50 placebo, 45 moxifloxacin). Peak placebo-corrected change from baseline for QTcI with tbo-filgrastim was 3.5 milliseconds, with a two-sided 95% upper confidence interval of 7.2 milliseconds, demonstrating no signal for any tbo-filgrastim effect on QTc. Concentration-effect modeling showed no evidence of an effect of tbo-filgrastim on cardiac repolarization. Tbo-filgrastim produced no clinically significant changes in other electrocardiogram parameters. Tbo-filgrastim was well tolerated.