Aim: Interferons (IFNs) have been identified as a potential treatment alternative for Coronavirus Disease 19 (COVID-19). This study assessed the safety, tolerability, bioavailability, and biological activity of inhaled interferon-α2b (IFN-α2b) in healthy adults. Methods: A double-blind, randomized, phase 1 clinical trial was conducted with two cohorts of healthy subjects aged 18-50 years old. The first cohort received 2.5 MIU of inhaled IFN-α2b twice daily for 10 days (n=6) or placebo (n=3); the second cohort received 5.0 MIU of inhaled IFN-α2b in a similar scheme (n=6) or placebo (n=3). The first two doses were administered in an Emergency Department, then participants completed their treatment at home. Safety was measured through vital signs, new symptoms, and laboratory tests. Tolerability was measured as the participant´s treatment acceptability. Bioavailability and biological activity were measured from serum IFNα levels and real-time quantitative PCR of interferon-induced genes in blood before and after treatments. Results: Exposure to inhaled IFN-α2b at 2.5 MIU or 5 MIU doses did not produce significant changes in participant vital signs, or elicit new symptoms, and standard hematological and biochemical blood measurements were comparable to those recorded in individuals who received placebo. All adverse events were mild or moderate and did not require medical care. Participants reported very high tolerability. A dose-dependent mild increase in serum IFN-α concentrations and an increase in serum RNA expression of IFN-induced genes were observed after treatment. Conclusion: Inhaled IFN-α2b was safe, well-tolerated, and induced systemic biological activity in healthy subjects.