Background: Monocyte-derived macrophages or dendritic cells are of increasing interest for cellular therapeutic products to treat inflammation-related diseases and cancer. However, the isolation method and the culture conditions applied influence the functionality of cells. For some approaches, the adhesion-induced differentiation into macrophages must be prevented to maintain functions attributed to circulating monocytes. The effects of the isolation method on the functionality of non-adherent peripheral monocytes have not yet been investigated. Methods: The present study examines the impact of the isolation method on cell viability, growth, metabolism, inflammation-induced cytokine response, migratory capacity, and adherence of non-adherent human peripheral monocytes. The monocytes were isolated by magnetic sorting using either positive or negative selection and cultured in cell-repellent plates. Results: The purity and yield of monocytes were higher after positive selection. However, the adherence and migratory capacity, cytokine response, and metabolic activity were decreased compared to negatively selected monocytes. The impaired functionality presented in combination with cell shrinking, thus, indicates the start of cell viability loss. Negatively selected non-adherent monocytes showed no impairment in functionality, and the viability remained high. In conclusion, this approach is better suited for conducting ex vivo modifications of monocytes prior to the intended experimental setup or therapeutic application.