Background: Although the olfactory epithelium, including its neuronal cell line, has inherent regenerative potential, therapeutic options remain limited. Promising effects of granulocyte colony stimulating factor (G-CSF) on olfactory regeneration have been observed in both animal and human studies. In this study, we assessed olfaction before and after G-CSF administration in myeloma patients who underwent autologous stem cell transplantation and in allogeneic stem cell donors. Methods: A total of 40 subjects were included in this study (10 myeloma patients, 10 allogeneic stem cell donors, 20 controls who did not receive any G-CSF). Olfactory function was psychophysically assessed using the threshold and extended identification domain of the Sniffin' Sticks test. Results: After G-CSF administration, threshold scores were slightly enhanced in both myeloma patients (8.9 ± 3.6 vs. 9.3 ± 3.3) and allogeneic stem cell donors (10.2 ± 3.5 vs. 11.8 ± 2.9). However, this effect was not statistically significant. For olfactory identification, no improvement was observed. Conclusion: Even though being not statistically significant, the findings of this study align with previous evidence and underline the potential of G-CSF on olfactory regeneration. However, additional studies, including carefully designed animal trials, are required to comprehensively evaluate this promising therapeutic option. Level of Evidence: 2.