Intoduction: Dental plaque harbors microorganisms that can enter the blood stream due to bacteremia, and reach heart prosthetic devices and become secondary septic foci. The presence of Mycoplasma in gingival-periodontal plaque and the ability of Mycoplasma to adhere to nitinol surfaces in cultures with horse serum have been documented. Human serum, a source of cholesterol, may promote Mycoplasma colonization of prosthetic devices.Objective: To study the effect of human serum on biofilm formation by Mycoplasma on Nitinol® surfaces, using scanning electron microscopy (SEM). Materials and methods:Sixty samples of nitinol were suspended in PPLO broth supplemented with 20% human serum, inoculated with Mycoplasma spp., and incubated under anaerobiosis for 5 days. The samples were then washed with sterile distilled water and processed for observation by SEM. Nitinol samples suspended in PPLO broth supplemented with 20% horse serum and inoculated with Mycoplasma spp. served as control.Results: Mycoplasma spp. formed biofilms on all nitinol surfaces; the biofilms mostly consisted of cells undergoing cell division. Given a 95% confidence interval and a sample size of n=60, the lower confidence bound on the percentage of positive cases was 94%. The results showed that human serum enhanced biofilm formation by Mycoplasma on nitinol surfaces.